diff --git a/BACKLOG.md b/BACKLOG.md
index 700ba11..406b239 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -26,14 +26,19 @@ What is left, most needed first. The detail is in the item each names.
 3. ~~**I3**~~ — done 2026-10-16: `ctl bench overhead`, figures in the
    README.
 4. ~~**I4**~~ — done 2026-10-17: several keys for one outside provider.
-5. **J2** — a judge the leader adds by itself is sized as init's is. (S)
-6. **J3** — HA setup puts the judges on nodes of their own. (S)
-7. **J8** — a judge budget that fits the machine, measured at install. (S)
-8. **F5** — large imports limited by the embedding engine's slots. (M)
-9. **I1** — answers to similar questions from the cache. (M)
-10. **J4** — the model mirror on more than one machine. (M)
-11. **I2** — the customer's MCP servers behind llmgw. (L)
-12. Smaller leftovers: audit before/after values, a tenant-admin role and
+5. ~~**Active Directory and Entra ID**~~ — done 2026-10-18: `auth.ldap`
+   sign-in and sync, Entra's 200-group overflow kept from taking roles.
+   Still to do: try it against a real domain controller (a Samba AD DC
+   on Proxmox): LDAPS, nested groups, a disabled user suspended by the
+   sync.
+6. **J2** — a judge the leader adds by itself is sized as init's is. (S)
+7. **J3** — HA setup puts the judges on nodes of their own. (S)
+8. **J8** — a judge budget that fits the machine, measured at install. (S)
+9. **F5** — large imports limited by the embedding engine's slots. (M)
+10. **I1** — answers to similar questions from the cache. (M)
+11. **J4** — the model mirror on more than one machine. (M)
+12. **I2** — the customer's MCP servers behind llmgw. (L)
+13. Smaller leftovers: audit before/after values, a tenant-admin role and
     forms hidden from viewers (C1); Parquet and a scheduled push for usage
     export (C4); English errors on Turkish pages (C24); H1 tried on the PoC;
     licences in video and audio (H5); nginx in front of several control
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d6a4e7..72b3663 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,13 @@ APIs change between minors without a deprecation period.
 
 ### Added
 
+- **Sign-in with Active Directory** (`auth.ldap`). People sign in on the gateway's form with their AD username or mail
+  and password, checked against the domain controllers over LDAPS or StartTLS. Groups, nested ones included, give
+  staff roles and places in the tree, as with OIDC. Accounts are tied to the `objectGUID` and made at first sign-in
+  when `create_accounts` is on. Every 15 minutes the leader reads the directory. People disabled or deleted there are
+  suspended and reinstated when they come back; roles and memberships follow their groups. A sync that would suspend
+  more than half the accounts is refused. See docs/install.md, "Active Directory".
+
 - **Several keys for one outside provider.** An external model takes `api_key_files`, each with an optional weight, in
   place of `api_key_file`. Each key is an endpoint of its own (`external:MODEL#1`, `#2`), so a key answering 429 is
   passed over while its breaker is open and the request goes to another. A key answering 401 is passed over too, and
@@ -41,6 +48,11 @@ APIs change between minors without a deprecation period.
 
 ### Fixed
 
+- **Entra ID's groups past 200 no longer take a role away.** For someone in more than 200 groups Entra sends none in
+  the token, only a pointer to Graph. That was read as no groups, so an administrator lost their role at the next
+  sign-in. Their role and memberships are now left as they were, and an error is logged saying what to change in the app
+  registration. docs/install.md has an Entra ID section.
+- **An account made by SCIM or OIDC could not be reinstated.** Setting it active was refused as "never approved".
 - **An upgrade refits the judge an earlier `server init` installed.** Upgrading to v0.14.7 left such a judge as it was:
   no cores or one, 2 or 4 GB, the prompt cache on. On fewer than eight cores every request was refused until it was
   fixed by hand. Now the leader finds a judge whose entry is exactly what an earlier init wrote and gives it 2 GB, no
diff --git a/docs/install.md b/docs/install.md
index ffa72ba..ebc19dd 100644
--- a/docs/install.md
+++ b/docs/install.md
@@ -2541,6 +2541,82 @@ and point it at `https://<gateway>/scim/v2` with that token as the bearer.
   join and leave them. Membership in a group is removed when someone leaves
   it.
 
+### Entra ID
+
+Entra ID is an OpenID Connect provider like the others, with two things to
+set in the app registration:
+
+1. **Redirect URI:** under Authentication, add a Web platform with
+   `https://<gateway>/login/oidc/callback`. The issuer is
+   `https://login.microsoftonline.com/<tenant-id>/v2.0`.
+2. **Groups in the token:** under Token configuration, add a groups claim.
+   Choose **Groups assigned to the application**, and assign the groups you
+   map in `roles` and `memberships` to the enterprise application. Entra
+   sends groups by object id unless you choose to emit names
+   (`sAMAccountName` for groups synced from AD), so write them the same way
+   in the mapping.
+
+Entra leaves the groups out of the token for someone in more than 200 of
+them and sends a pointer to Graph instead. llmgw then keeps that person's
+role and memberships as they were, rather than reading it as no groups, and
+logs an error saying so. "Groups assigned to the application" avoids this.
+So does SCIM below, which Entra also speaks: in the enterprise application
+under Provisioning, set the tenant URL to `https://<gateway>/scim/v2` and
+the secret token to the contents of `auth.scim.token_file`.
+
+## Active Directory
+
+With an on-premises Active Directory, people sign in on the gateway's own
+form with their AD username (`ada`, `CORP\ada`, `ada@corp.example`) and
+password. The gateway checks them with the domain controllers over LDAPS:
+
+```yaml
+auth:
+  enabled: true
+  ldap:
+    urls: [ldaps://dc1.corp.example, ldaps://dc2.corp.example]   # tried in order
+    ca_file: /etc/llmgw/corp-ca.pem         # the domain's CA, when not in the system's
+    bind_dn: CN=svc-llmgw,OU=Service,DC=corp,DC=example
+    bind_password_file: /etc/llmgw/secrets/ldap-bind   # root-only
+    base_dn: OU=Staff,DC=corp,DC=example    # where people are
+    user_filter: (memberOf:1.2.840.113556.1.4.1941:=CN=llmgw-users,OU=Groups,DC=corp,DC=example)
+    label: Acme                             # "Sign in with your Acme account"
+    create_accounts: true
+    roles:                                  # by group CN or full DN; nested groups count
+      admin: [llmgw-admins]
+      operator: [llmgw-ops]
+    memberships:
+      ml-engineers: "team:Acme/ml"
+    sync_interval: 15m                      # negative turns the sync off
+```
+
+- **Service account:** an ordinary domain user is enough: it only reads.
+  It finds the person and reads their groups. The person's password is
+  checked by binding as them, and is never stored.
+- **Encryption:** `ldaps://`, or `ldap://` with `start_tls: true`.
+  Plaintext LDAP is refused, since passwords would cross the network.
+- **Who may sign in:** enabled user objects under `base_dn` that match
+  `user_filter`. The example admits members of `llmgw-users`, nested groups
+  included.
+- **Accounts:** an account is tied to the person's `objectGUID`, so a changed
+  mail or name is still the same account. An account that already exists
+  with the person's mail is taken over. Without `create_accounts`, only
+  people who already have an account can sign in. Local accounts, such as
+  the administrator `server init` made, keep signing in with their own
+  password.
+- **Sync:** every `sync_interval` the leader reads the directory.
+  - Someone disabled or deleted in AD is suspended and their sessions
+    end.
+  - When they are enabled again they are reinstated. An account an
+    administrator suspended by hand stays suspended.
+  - Roles follow groups, and memberships the directory gave are taken away
+    when the person leaves the group.
+  - A sync that would suspend more than half of the directory's accounts is
+    refused and logged, rather than locking everyone out over a wrong
+    `base_dn` or filter.
+- **Passwords:** a person's password is changed in AD. The gateway sends no
+  reset link for these accounts.
+
 ## Secrets in Vault
 
 Every setting that names a file holding a secret — the store's `@address`,
diff --git a/docs/reference.md b/docs/reference.md
index 9e1a0f1..859c950 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -37,6 +37,7 @@ rather than repeated.
 | `default_tpm` | `int` | [Auth](#auth) |
 | `signup_open` | `bool` | [Auth](#auth) |
 | `oidc` | `OIDC` | [Auth](#auth) |
+| `ldap` | `LDAP` | [Auth](#auth) |
 | `scim` | `SCIM` | [Auth](#auth) |
 | `max_key_ttl` | `time.Duration` | [Auth](#auth) |
 | `personal` | `Personal` | [Auth](#auth) |
@@ -147,6 +148,20 @@ rather than repeated.
 | `tokenize_timeout` | `time.Duration` | [KVIndex](#kvindex) |
 | `min_blocks` | `int` | [KVIndex](#kvindex) |
 | `max_blocks` | `int` | [KVIndex](#kvindex) |
+| `urls` | `[]string` | [LDAP](#ldap) |
+| `start_tls` | `bool` | [LDAP](#ldap) |
+| `ca_file` | `string` | [LDAP](#ldap) |
+| `bind_dn` | `string` | [LDAP](#ldap) |
+| `bind_password_file` | `string` | [LDAP](#ldap) |
+| `base_dn` | `string` | [LDAP](#ldap) |
+| `group_base_dn` | `string` | [LDAP](#ldap) |
+| `user_filter` | `string` | [LDAP](#ldap) |
+| `label` | `string` | [LDAP](#ldap) |
+| `create_accounts` | `bool` | [LDAP](#ldap) |
+| `roles` | `map[string][]string` | [LDAP](#ldap) |
+| `memberships` | `map[string]string` | [LDAP](#ldap) |
+| `sync_interval` | `time.Duration` | [LDAP](#ldap) |
+| `timeout` | `time.Duration` | [LDAP](#ldap) |
 | `contact` | `string` | [Landing](#landing) |
 | `notice` | `string` | [Landing](#landing) |
 | `language` | `string` | [Landing](#landing) |
@@ -619,6 +634,15 @@ OIDC is sign-in through an identity provider.
 
 Takes a [OIDC](#oidc) block.
 
+### `ldap`
+
+`LDAP`
+
+LDAP is sign-in against a directory, Active Directory above all, and
+the accounts kept in step with it.
+
+Takes a [LDAP](#ldap) block.
+
 ### `scim`
 
 `SCIM`
@@ -1427,6 +1451,106 @@ MaxBlocks bounds how many of a prompt's blocks are hashed and looked
 up. Beyond it a longer match still helps, but the difference no longer
 decides anything. Zero takes 4096.
 
+## LDAP
+
+### `urls`
+
+`[]string`
+
+URLs are the directory's servers, tried in turn: ldaps:// (636), or
+ldap:// (389) with StartTLS.
+
+### `start_tls`
+
+`bool`
+
+StartTLS upgrades an ldap:// connection before anything is sent. A
+password never crosses a connection without TLS: ldap:// without it
+is refused.
+
+### `ca_file`
+
+`string`
+
+CAFile is the authority the servers' certificates are checked against,
+when it is not the system's: an AD Certificate Services root.
+
+### `bind_dn`
+
+`string`
+
+BindDN and the file holding its password: a service account that may
+read users and groups. Nothing is written to the directory.
+
+### `bind_password_file`
+
+`string`
+
+### `base_dn`
+
+`string`
+
+BaseDN is where people are searched for, subtree included.
+
+### `group_base_dn`
+
+`string`
+
+GroupBaseDN is where their groups are; empty is BaseDN's domain root.
+
+### `user_filter`
+
+`string`
+
+UserFilter narrows who may sign in, ANDed with the login match: a
+group (memberOf=...) or an OU's people only. Empty is every enabled
+user object.
+
+### `label`
+
+`string`
+
+Label is what the form says to sign in with: "Sign in with your
+<label> account". Empty is "Active Directory".
+
+### `create_accounts`
+
+`bool`
+
+CreateAccounts makes an account, active, for a person the directory
+vouches for and the gateway does not know. Off, only existing accounts
+sign in this way.
+
+### `roles`
+
+`map[string][]string`
+
+Roles maps a staff role (viewer, operator, billing, admin) to the
+groups that give it, by name (CN) or whole DN. Set at every sign-in
+and sync: someone taken out of the group loses the role.
+
+### `memberships`
+
+`map[string]string`
+
+Memberships maps a group, by CN or DN, to a place in the tree —
+org:NAME, team:ORG/TEAM, project:ORG/TEAM/PROJECT — joined at sign-in
+and kept by the sync, which also takes away a place whose group the
+person has left.
+
+### `sync_interval`
+
+`time.Duration`
+
+SyncInterval is how often the leader reads the directory. Zero is
+15m; negative turns the sync off, leaving only sign-in.
+
+### `timeout`
+
+`time.Duration`
+
+Timeout bounds each round trip to a server. Zero is 10s.
+
 ## Landing
 
 ### `contact`
diff --git a/go.mod b/go.mod
index 13d3ebc..5b6eaea 100644
--- a/go.mod
+++ b/go.mod
@@ -12,6 +12,7 @@ require (
 	github.com/charmbracelet/x/ansi v0.11.6
 	github.com/coreos/go-oidc/v3 v3.21.0
 	github.com/go-jose/go-jose/v4 v4.1.4
+	github.com/go-ldap/ldap/v3 v3.4.15
 	github.com/go-zeromq/zmq4 v0.17.0
 	github.com/jackc/pgx/v5 v5.11.0
 	github.com/knadh/koanf/parsers/yaml v1.1.1
@@ -45,6 +46,7 @@ require (
 require (
 	filippo.io/edwards25519 v1.2.0 // indirect
 	filippo.io/hpke v0.4.0 // indirect
+	github.com/Azure/go-ntlmssp v0.1.1 // indirect
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
@@ -57,6 +59,7 @@ require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
+	github.com/go-asn1-ber/asn1-ber v1.5.8 // indirect
 	github.com/go-logr/logr v1.4.4 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.5.0 // indirect
diff --git a/go.sum b/go.sum
index f47ac0c..d6f56b5 100644
--- a/go.sum
+++ b/go.sum
@@ -8,8 +8,12 @@ filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
 filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
 filippo.io/hpke v0.4.0 h1:p575VVQ6ted4pL+it6M00V/f2qTZITO0zgmdKCkd5+A=
 filippo.io/hpke v0.4.0/go.mod h1:EmAN849/P3qdeK+PCMkDpDm83vRHM5cDipBJ8xbQLVY=
+github.com/Azure/go-ntlmssp v0.1.1 h1:l+FM/EEMb0U9QZE7mKNEDw5Mu3mFiaa2GKOoTSsNDPw=
+github.com/Azure/go-ntlmssp v0.1.1/go.mod h1:NYqdhxd/8aAct/s4qSYZEerdPuH1liG2/X9DiVTbhpk=
 github.com/NVIDIA/go-nvml v0.13.4-0 h1:o3jp9u2x1R9ShFE3v+Aesp55XOSIQFMJz/VGNUcJaNE=
 github.com/NVIDIA/go-nvml v0.13.4-0/go.mod h1:id63qwpoDWpFXwnwM6psDCSqW4BmNu6mWpr4YeQtPGo=
+github.com/alexbrainman/sspi v0.0.0-20250919150558-7d374ff0d59e h1:4dAU9FXIyQktpoUAgOJK3OTFc/xug0PCXYCqU0FgDKI=
+github.com/alexbrainman/sspi v0.0.0-20250919150558-7d374ff0d59e/go.mod h1:cEWa1LVoE5KvSD9ONXsZrj0z6KqySlCCNKHlLzbqAt4=
 github.com/aymanbagabas/go-osc52/v2 v2.0.1 h1:HwpRHbFMcZLEVr42D4p7XBqjyuxQH5SMiErDT4WkJ2k=
 github.com/aymanbagabas/go-osc52/v2 v2.0.1/go.mod h1:uYgXzlJ7ZpABp8OJ+exZzJJhRNQ2ASbcXHWsFqH8hp8=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
@@ -46,8 +50,12 @@ github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f h1:Y/CXytFA4m6
 github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f/go.mod h1:vw97MGsxSvLiUE2X8qFplwetxpGLQrlU1Q9AUEIzCaM=
 github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
 github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
+github.com/go-asn1-ber/asn1-ber v1.5.8 h1:H9AZkK22UOmfX8J84ubyaZxKJZ3FMHVwn8swoMML7iQ=
+github.com/go-asn1-ber/asn1-ber v1.5.8/go.mod h1:hEBeB/ic+5LoWskz+yKT7vGhhPYkProFKoKdwZRWMe0=
 github.com/go-jose/go-jose/v4 v4.1.4 h1:moDMcTHmvE6Groj34emNPLs/qtYXRVcd6S7NHbHz3kA=
 github.com/go-jose/go-jose/v4 v4.1.4/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
+github.com/go-ldap/ldap/v3 v3.4.15 h1:eRB4f4Ecn1POL1mO86+uUDlecmyWsdiJwh60bAUS4UY=
+github.com/go-ldap/ldap/v3 v3.4.15/go.mod h1:jeD0c98EdZQCKKKKe4kTWs5aCf6y+j8KuYsYLznZSQk=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
 github.com/go-logr/logr v1.4.4 h1:tG4xh9yMsRCAiodLVTxyrkzSZ9+o0L1Kg/+cPVcbP/8=
 github.com/go-logr/logr v1.4.4/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
@@ -69,6 +77,8 @@ github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.30.0 h1:/Tnpcb2E0Pz/tN9s3bfEY2Q8ePCEX9iuS+cneUwncnw=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.30.0/go.mod h1:zOBXOsUaBSjKgmH4OGzV1esUpR3oUSCPYVd2cUBjKYY=
+github.com/hashicorp/go-uuid v1.0.3 h1:2gKiV6YVmrJ1i2CKKa9obLvRieoRGviZFL26PcT/Co8=
+github.com/hashicorp/go-uuid v1.0.3/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
 github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
 github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
@@ -81,6 +91,18 @@ github.com/jackc/pgx/v5 v5.11.0 h1:IzBBtyK9AHqf98cctWFifYSci2hgQR/cd56wB4p+ogg=
 github.com/jackc/pgx/v5 v5.11.0/go.mod h1:mal1tBGAFfLHvZzaYh77YS/eC6IX9OWbRV1QIIM0Jn4=
 github.com/jackc/puddle/v2 v2.2.2 h1:PR8nw+E/1w0GLuRFSmiioY6UooMp6KJv0/61nB7icHo=
 github.com/jackc/puddle/v2 v2.2.2/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/jcmturner/aescts/v2 v2.0.0 h1:9YKLH6ey7H4eDBXW8khjYslgyqG2xZikXP0EQFKrle8=
+github.com/jcmturner/aescts/v2 v2.0.0/go.mod h1:AiaICIRyfYg35RUkr8yESTqvSy7csK90qZ5xfvvsoNs=
+github.com/jcmturner/dnsutils/v2 v2.0.0 h1:lltnkeZGL0wILNvrNiVCR6Ro5PGU/SeBvVO/8c/iPbo=
+github.com/jcmturner/dnsutils/v2 v2.0.0/go.mod h1:b0TnjGOvI/n42bZa+hmXL+kFJZsFT7G4t3HTlQ184QM=
+github.com/jcmturner/gofork v1.7.6 h1:QH0l3hzAU1tfT3rZCnW5zXl+orbkNMMRGJfdJjHVETg=
+github.com/jcmturner/gofork v1.7.6/go.mod h1:1622LH6i/EZqLloHfE7IeZ0uEJwMSUyQ/nDd82IeqRo=
+github.com/jcmturner/goidentity/v6 v6.0.1 h1:VKnZd2oEIMorCTsFBnJWbExfNN7yZr3EhJAxwOkZg6o=
+github.com/jcmturner/goidentity/v6 v6.0.1/go.mod h1:X1YW3bgtvwAXju7V3LCIMpY0Gbxyjn/mY9zx4tFonSg=
+github.com/jcmturner/gokrb5/v8 v8.4.4 h1:x1Sv4HaTpepFkXbt2IkL29DXRf8sOfZXo8eRKh687T8=
+github.com/jcmturner/gokrb5/v8 v8.4.4/go.mod h1:1btQEpgT6k+unzCwX1KdWMEwPPkkgBtP+F6aCACiMrs=
+github.com/jcmturner/rpc/v2 v2.0.3 h1:7FXXj8Ti1IaVFpSAziCZWNzbNuZmnvw/i6CqLNdWfZY=
+github.com/jcmturner/rpc/v2 v2.0.3/go.mod h1:VUJYCIDm3PVOEHw8sgt091/20OJjskO/YJki3ELg/Hc=
 github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
 github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=
 github.com/knadh/koanf/maps v0.1.2 h1:RBfmAW5CnZT+PJ1CVc1QSJKf4Xu9kxfQgYVQSu8hpbo=
diff --git a/internal/account/directory_test.go b/internal/account/directory_test.go
new file mode 100644
index 0000000..d536faa
--- /dev/null
+++ b/internal/account/directory_test.go
@@ -0,0 +1,63 @@
+package account
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/store"
+)
+
+type fakeDirectory struct {
+	asked []string
+	u     store.User
+	err   error
+}
+
+func (f *fakeDirectory) SignIn(_ context.Context, login, _ string) (store.User, error) {
+	f.asked = append(f.asked, login)
+	return f.u, f.err
+}
+
+// With a directory, a name the store has no password for is the
+// directory's to check; an account with a password here — the
+// administrator init made — is still checked here, so a directory that is
+// down locks nobody out.
+func TestPasswordsKeptElsewhereAreTheDirectorysToCheck(t *testing.T) {
+	svc, st := newService(t)
+	ctx := t.Context()
+	hash, _ := HashPassword("local-secret")
+	admin := store.User{ID: "usr-admin", Email: "admin@example.com", Name: "a", PasswordHash: hash,
+		State: store.UserActive, CreatedAt: time.Now()}
+	ada := store.User{ID: "usr-ada", Email: "ada@corp.example", Name: "Ada", PasswordHash: "!ldap",
+		State: store.UserActive, CreatedAt: time.Now()}
+	for _, u := range []store.User{admin, ada} {
+		if err := st.CreateUser(ctx, u); err != nil {
+			t.Fatal(err)
+		}
+	}
+	dir := &fakeDirectory{u: ada}
+	svc.SetDirectory(dir)
+
+	if _, _, err := svc.SignIn(ctx, "admin@example.com", "local-secret"); err != nil || len(dir.asked) != 0 {
+		t.Fatalf("the local administrator: %v, directory asked %v", err, dir.asked)
+	}
+	// A name, not an address, and an account kept by the directory.
+	for _, login := range []string{`CORP\ada`, "ada@corp.example"} {
+		if tok, _, err := svc.SignIn(ctx, login, "ad-secret"); err != nil || tok == "" {
+			t.Errorf("%s: %v", login, err)
+		}
+	}
+	if len(dir.asked) != 2 || dir.asked[0] != `CORP\ada` {
+		t.Errorf("the directory was asked %v", dir.asked)
+	}
+	dir.err = ErrBadCredentials
+	if _, _, err := svc.SignIn(ctx, "ada", "wrong"); !errors.Is(err, ErrBadCredentials) {
+		t.Errorf("a password the directory refused: %v", err)
+	}
+	// A reset link would give a directory's account a password here.
+	if _, _, err := svc.RequestReset(ctx, st, "ada@corp.example"); !errors.Is(err, ErrNoReset) {
+		t.Errorf("a directory's account was sent a reset link: %v", err)
+	}
+}
diff --git a/internal/account/service.go b/internal/account/service.go
index 20af403..3ff25d0 100644
--- a/internal/account/service.go
+++ b/internal/account/service.go
@@ -80,8 +80,26 @@ type Service struct {
 
 	mu       sync.Mutex
 	attempts map[string]*attemptWindow
+
+	// dir checks the passwords of accounts this store keeps none for.
+	dir Directory
 }
 
+// Directory checks a password against an outside directory — Active
+// Directory over LDAP — and answers the account to sign in: made or kept in
+// step with the directory. Its errors are this package's ErrBadCredentials
+// and ErrSuspended for the person's own, and anything else for the
+// directory's.
+type Directory interface {
+	SignIn(ctx context.Context, login, password string) (store.User, error)
+}
+
+// SetDirectory has passwords for accounts with none here, and names that are
+// not addresses, checked by the directory. An account with a password here
+// — the administrator init made — is still checked here, so a directory that
+// is down locks nobody out.
+func (s *Service) SetDirectory(d Directory) { s.dir = d }
+
 type attemptWindow struct {
 	count int
 	since time.Time
@@ -137,6 +155,7 @@ func (s *Service) SignUp(ctx context.Context, email, name, password string) erro
 // SignIn checks a password and opens a session, returning the session token and
 // the CSRF token that must accompany the forms in it.
 func (s *Service) SignIn(ctx context.Context, email, password string) (token, csrf string, err error) {
+	login := strings.TrimSpace(email)
 	email = store.NormalizeEmail(email)
 	// Counted per address and the client trying it, so somebody guessing
 	// from elsewhere cannot lock the owner out of their own account; and per
@@ -151,6 +170,15 @@ func (s *Service) SignIn(ctx context.Context, email, password string) (token, cs
 	}
 
 	u, err := s.store.UserByEmail(ctx, email)
+	// No password kept here — the directory's, or nobody's — and a
+	// directory to ask: it decides.
+	if s.dir != nil && (errors.Is(err, store.ErrNotFound) || (err == nil && strings.HasPrefix(u.PasswordHash, "!"))) {
+		if u, err = s.dir.SignIn(ctx, login, password); err != nil {
+			return "", "", err
+		}
+		s.clearAttempts(byClient)
+		return s.open(ctx, u)
+	}
 	if errors.Is(err, store.ErrNotFound) {
 		// Verify anyway, against a hash that cannot match. Returning early here
 		// would let a stopwatch enumerate every account on the system.
@@ -180,7 +208,11 @@ func (s *Service) SignIn(ctx context.Context, email, password string) (token, cs
 	case store.UserSuspended:
 		return "", "", ErrSuspended
 	}
+	return s.open(ctx, u)
+}
 
+// open makes a session for a person whose password was right.
+func (s *Service) open(ctx context.Context, u store.User) (token, csrf string, err error) {
 	if token, err = store.NewSessionToken(); err != nil {
 		return "", "", err
 	}
@@ -402,7 +434,10 @@ func (s *Service) RequestReset(ctx context.Context, rs ResetStore, email string)
 		return "", store.User{}, ErrTooManyTries
 	}
 	u, err := rs.UserByEmail(ctx, email)
-	if err != nil || u.PasswordHash == "" || u.State != store.UserActive {
+	// An account whose password is kept elsewhere — "!oidc", "!scim",
+	// "!ldap" — gets no link: setting one here would give it a second way
+	// in that its directory knows nothing of, and outlives its leaving.
+	if err != nil || u.PasswordHash == "" || strings.HasPrefix(u.PasswordHash, "!") || u.State != store.UserActive {
 		return "", store.User{}, ErrNoReset
 	}
 	token, err := rs.CreatePasswordReset(ctx, u.ID, ResetLinkTTL)
diff --git a/internal/config/config.go b/internal/config/config.go
index decabfd..9662cd7 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -442,6 +442,9 @@ type Auth struct {
 
 	// OIDC is sign-in through an identity provider.
 	OIDC OIDC `koanf:"oidc"`
+	// LDAP is sign-in against a directory, Active Directory above all, and
+	// the accounts kept in step with it.
+	LDAP LDAP `koanf:"ldap"`
 	// SCIM is account provisioning by the identity provider.
 	SCIM SCIM `koanf:"scim"`
 
@@ -968,6 +971,12 @@ func (s Server) Validate() error {
 	if err := s.Auth.OIDC.Validate(); err != nil {
 		return err
 	}
+	if err := s.Auth.LDAP.Validate(); err != nil {
+		return err
+	}
+	if s.Auth.LDAP.Enabled() && !s.Auth.Enabled {
+		return fmt.Errorf("auth.ldap needs auth.enabled: it signs people in to the accounts the store keeps")
+	}
 	if err := s.AgentTLS.Validate(); err != nil {
 		return err
 	}
diff --git a/internal/config/ldap.go b/internal/config/ldap.go
new file mode 100644
index 0000000..c442a39
--- /dev/null
+++ b/internal/config/ldap.go
@@ -0,0 +1,137 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// LDAP is sign-in against a directory — Active Directory above all — with
+// the directory's own passwords, and the accounts kept in step with it.
+//
+//	auth:
+//	  ldap:
+//	    urls: [ldaps://dc1.corp.example.com, ldaps://dc2.corp.example.com]
+//	    bind_dn: CN=llmgw,OU=Service Accounts,DC=corp,DC=example,DC=com
+//	    bind_password_file: /etc/llmgw/secrets/ldap-bind
+//	    base_dn: OU=Staff,DC=corp,DC=example,DC=com
+//	    create_accounts: true
+//	    roles: {admin: [llmgw-admins]}
+//	    memberships: {ml-team: "team:Acme/ml"}
+//
+// A person signs in on the portal's form with their sAMAccountName, their
+// userPrincipalName or their mail, and their directory password. The
+// gateway finds them with the bind account, checks the password by binding
+// as them, and reads their groups, nested ones included. Every sync_interval
+// the leader reads the directory again: an account disabled or gone there
+// is suspended here, its sessions ended and its API keys refused.
+type LDAP struct {
+	// URLs are the directory's servers, tried in turn: ldaps:// (636), or
+	// ldap:// (389) with StartTLS.
+	URLs []string `koanf:"urls"`
+	// StartTLS upgrades an ldap:// connection before anything is sent. A
+	// password never crosses a connection without TLS: ldap:// without it
+	// is refused.
+	StartTLS bool `koanf:"start_tls"`
+	// CAFile is the authority the servers' certificates are checked against,
+	// when it is not the system's: an AD Certificate Services root.
+	CAFile string `koanf:"ca_file"`
+	// BindDN and the file holding its password: a service account that may
+	// read users and groups. Nothing is written to the directory.
+	BindDN           string `koanf:"bind_dn"`
+	BindPasswordFile string `koanf:"bind_password_file"`
+	// BaseDN is where people are searched for, subtree included.
+	BaseDN string `koanf:"base_dn"`
+	// GroupBaseDN is where their groups are; empty is BaseDN's domain root.
+	GroupBaseDN string `koanf:"group_base_dn"`
+	// UserFilter narrows who may sign in, ANDed with the login match: a
+	// group (memberOf=...) or an OU's people only. Empty is every enabled
+	// user object.
+	UserFilter string `koanf:"user_filter"`
+	// Label is what the form says to sign in with: "Sign in with your
+	// <label> account". Empty is "Active Directory".
+	Label string `koanf:"label"`
+	// CreateAccounts makes an account, active, for a person the directory
+	// vouches for and the gateway does not know. Off, only existing accounts
+	// sign in this way.
+	CreateAccounts bool `koanf:"create_accounts"`
+	// Roles maps a staff role (viewer, operator, billing, admin) to the
+	// groups that give it, by name (CN) or whole DN. Set at every sign-in
+	// and sync: someone taken out of the group loses the role.
+	Roles map[string][]string `koanf:"roles"`
+	// Memberships maps a group, by CN or DN, to a place in the tree —
+	// org:NAME, team:ORG/TEAM, project:ORG/TEAM/PROJECT — joined at sign-in
+	// and kept by the sync, which also takes away a place whose group the
+	// person has left.
+	Memberships map[string]string `koanf:"memberships"`
+	// SyncInterval is how often the leader reads the directory. Zero is
+	// 15m; negative turns the sync off, leaving only sign-in.
+	SyncInterval time.Duration `koanf:"sync_interval"`
+	// Timeout bounds each round trip to a server. Zero is 10s.
+	Timeout time.Duration `koanf:"timeout"`
+}
+
+// Enabled reports whether directory sign-in is configured.
+func (l LDAP) Enabled() bool { return len(l.URLs) > 0 }
+
+// Validate says what in the configuration cannot work.
+func (l LDAP) Validate() error {
+	if !l.Enabled() {
+		return nil
+	}
+	for _, raw := range l.URLs {
+		u, err := url.Parse(raw)
+		if err != nil || u.Host == "" {
+			return fmt.Errorf("auth.ldap.urls: %q is not an ldap:// or ldaps:// address", raw)
+		}
+		switch u.Scheme {
+		case "ldaps":
+		case "ldap":
+			if !l.StartTLS {
+				return fmt.Errorf("auth.ldap.urls: %q is plaintext: use ldaps://, or set start_tls; passwords would cross it", raw)
+			}
+		default:
+			return fmt.Errorf("auth.ldap.urls: %q is not an ldap:// or ldaps:// address", raw)
+		}
+	}
+	switch {
+	case strings.TrimSpace(l.BindDN) == "" || l.BindPasswordFile == "":
+		return errors.New("auth.ldap: bind_dn and bind_password_file are needed, for the account that finds people")
+	case strings.TrimSpace(l.BaseDN) == "":
+		return errors.New("auth.ldap: base_dn is needed, where people are searched for")
+	case l.UserFilter != "" && !(strings.HasPrefix(l.UserFilter, "(") && strings.HasSuffix(l.UserFilter, ")")):
+		return fmt.Errorf("auth.ldap.user_filter: %q is not an LDAP filter in parentheses", l.UserFilter)
+	}
+	for role := range l.Roles {
+		if !validStaffRole(role) {
+			return fmt.Errorf("auth.ldap.roles: %q is not viewer, operator, billing or admin", role)
+		}
+	}
+	for g, place := range l.Memberships {
+		if !validPlace(place) {
+			return fmt.Errorf("auth.ldap.memberships[%s]: %q is not org:NAME, team:ORG/TEAM or project:ORG/TEAM/PROJECT", g, place)
+		}
+	}
+	return nil
+}
+
+// Interval is SyncInterval with its default; zero means off.
+func (l LDAP) Interval() time.Duration {
+	switch {
+	case l.SyncInterval < 0:
+		return 0
+	case l.SyncInterval == 0:
+		return 15 * time.Minute
+	}
+	return l.SyncInterval
+}
+
+// RoundTrip is Timeout with its default.
+func (l LDAP) RoundTrip() time.Duration {
+	if l.Timeout <= 0 {
+		return 10 * time.Second
+	}
+	return l.Timeout
+}
diff --git a/internal/config/oidc.go b/internal/config/oidc.go
index 4373cd7..d4d58c5 100644
--- a/internal/config/oidc.go
+++ b/internal/config/oidc.go
@@ -72,21 +72,34 @@ func (o OIDC) Validate() error {
 		return errors.New("auth.oidc.client_id is required")
 	}
 	for role := range o.Roles {
-		switch role {
-		case "viewer", "operator", "billing", "admin":
-		default:
+		if !validStaffRole(role) {
 			return fmt.Errorf("auth.oidc.roles: %q is not viewer, operator, billing or admin", role)
 		}
 	}
 	for g, where := range o.Memberships {
-		kind, path, ok := strings.Cut(where, ":")
-		if !ok || path == "" || (kind != "org" && kind != "team" && kind != "project") {
+		if !validPlace(where) {
 			return fmt.Errorf("auth.oidc.memberships.%s is %q: org:NAME, team:ORG/TEAM or project:ORG/TEAM/PROJECT", g, where)
 		}
 	}
 	return nil
 }
 
+// validStaffRole is a role groups may give: viewer, operator, billing, admin.
+func validStaffRole(role string) bool {
+	switch role {
+	case "viewer", "operator", "billing", "admin":
+		return true
+	}
+	return false
+}
+
+// validPlace is a place in the tree a group may give: org:NAME,
+// team:ORG/TEAM or project:ORG/TEAM/PROJECT.
+func validPlace(where string) bool {
+	kind, path, ok := strings.Cut(where, ":")
+	return ok && path != "" && (kind == "org" || kind == "team" || kind == "project")
+}
+
 // SCIM lets an identity provider provision accounts (/scim/v2): made,
 // suspended and reinstated as they are there, with groups mapped by
 // auth.oidc's roles and memberships.
diff --git a/internal/directory/directory.go b/internal/directory/directory.go
new file mode 100644
index 0000000..f64c1ee
--- /dev/null
+++ b/internal/directory/directory.go
@@ -0,0 +1,395 @@
+// Package directory keeps accounts in step with an outside directory —
+// Active Directory over LDAP — at sign-in and by a periodic sync: made for
+// people the directory vouches for, given the staff role and the places in
+// the tree their groups map to, and suspended when the directory disables or
+// loses them.
+package directory
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"slices"
+	"strings"
+	"time"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/store"
+)
+
+// Identity is a person as the directory has them.
+type Identity struct {
+	// ID never changes for the person: an AD objectGUID.
+	ID    string
+	DN    string
+	Email string
+	Name  string
+	// Groups are the person's groups, nested ones included, each by its CN
+	// and by its DN, so a mapping may name either.
+	Groups []string
+	// Disabled is an account the directory has turned off.
+	Disabled bool
+}
+
+// Mapping is what a person's groups give them: a staff role and places in
+// the tree. The same shape as auth.oidc's.
+type Mapping struct {
+	Roles       map[string][]string
+	Memberships map[string]string
+}
+
+// Role is the highest staff role the groups give, "" when none.
+func (m Mapping) Role(groups []string) string {
+	for _, r := range []string{store.RoleAdmin, store.RoleOperator, store.RoleBilling, store.RoleViewer} {
+		if slices.ContainsFunc(m.Roles[r], func(g string) bool { return hasGroup(groups, g) }) {
+			return r
+		}
+	}
+	return ""
+}
+
+// Places are the places in the tree the groups give, each once.
+func (m Mapping) Places(groups []string) []string {
+	var out []string
+	for g, where := range m.Memberships {
+		if hasGroup(groups, g) && !slices.Contains(out, where) {
+			out = append(out, where)
+		}
+	}
+	slices.Sort(out)
+	return out
+}
+
+// Groups are every group the mapping names.
+func (m Mapping) Groups() []string {
+	var out []string
+	add := func(g string) {
+		if !slices.ContainsFunc(out, func(o string) bool { return strings.EqualFold(o, g) }) {
+			out = append(out, g)
+		}
+	}
+	for _, gs := range m.Roles {
+		for _, g := range gs {
+			add(g)
+		}
+	}
+	for g := range m.Memberships {
+		add(g)
+	}
+	slices.Sort(out)
+	return out
+}
+
+// hasGroup matches a group's CN or DN as AD does: case aside.
+func hasGroup(groups []string, g string) bool {
+	return slices.ContainsFunc(groups, func(have string) bool { return strings.EqualFold(have, g) })
+}
+
+// Store is what keeping accounts needs of the store.
+type Store interface {
+	UserByEmail(ctx context.Context, email string) (store.User, error)
+	UserByID(ctx context.Context, id string) (store.User, error)
+	CreateUser(ctx context.Context, u store.User) error
+	SetStaffRole(ctx context.Context, id, role string) error
+	SetUserState(ctx context.Context, id string, state store.UserState) error
+	DeleteUserSessions(ctx context.Context, userID string) error
+	AddMembership(ctx context.Context, user string, scope store.Scope, id, role, by string, at time.Time) error
+	RemoveMembership(ctx context.Context, userID string, scope store.Scope, scopeID string, at time.Time) (int, error)
+	MembershipsOf(ctx context.Context, userID string) ([]store.Membership, error)
+	AllOrgs(ctx context.Context) ([]store.Org, error)
+	AllTeams(ctx context.Context) ([]store.TeamPath, error)
+	AllProjects(ctx context.Context) ([]store.ProjectPath, error)
+	DirectoryUser(ctx context.Context, directory, externalID string) (store.DirectoryLink, error)
+	LinkDirectory(ctx context.Context, userID, directory, externalID string, at time.Time) error
+	DirectoryLinks(ctx context.Context, directory string) ([]store.DirectoryLink, error)
+	SetSyncSuspended(ctx context.Context, userID string, suspended bool, at time.Time) error
+}
+
+// Keeper keeps one directory's accounts.
+type Keeper struct {
+	St Store
+	// Name is the directory's, as links and memberships record it: "ldap".
+	Name           string
+	Mapping        Mapping
+	CreateAccounts bool
+	Now            func() time.Time
+}
+
+// The ways a person the directory vouches for is still refused.
+var (
+	ErrNoAccount = errors.New("no account here, and accounts are not made for the directory's people")
+	ErrSuspended = errors.New("the account is suspended here")
+	ErrNotActive = errors.New("the account is not active here")
+	ErrNoEmail   = errors.New("the directory has no mail for this person")
+	// ErrImplausible is a sync that would suspend too many at once: done
+	// nothing, and said.
+	ErrImplausible = errors.New("the directory's answer is implausible; nobody was suspended")
+)
+
+func (k *Keeper) now() time.Time {
+	if k.Now != nil {
+		return k.Now()
+	}
+	return time.Now()
+}
+
+// SignIn is the account for a person the directory has just vouched for:
+// found by their directory id, else their mail, else made; given what their
+// groups map to; refused when it may not sign in.
+func (k *Keeper) SignIn(ctx context.Context, id Identity) (store.User, error) {
+	u, link, err := k.account(ctx, id)
+	if err != nil {
+		return store.User{}, err
+	}
+	// The directory has them enabled, or the bind would have failed: an
+	// account the sync suspended for being disabled there is theirs again.
+	if u.State == store.UserSuspended && link.SuspendedBySync {
+		if u, err = k.reinstate(ctx, u); err != nil {
+			return store.User{}, err
+		}
+	}
+	switch {
+	case u.State == store.UserSuspended:
+		return store.User{}, ErrSuspended
+	case !u.CanSignIn():
+		return store.User{}, fmt.Errorf("%w: %s", ErrNotActive, u.State)
+	}
+	if err := k.apply(ctx, &u, id, false); err != nil {
+		return store.User{}, err
+	}
+	return u, nil
+}
+
+// account finds or makes the account and links it to the directory.
+func (k *Keeper) account(ctx context.Context, id Identity) (store.User, store.DirectoryLink, error) {
+	link, err := k.St.DirectoryUser(ctx, k.Name, id.ID)
+	switch {
+	case err == nil:
+		u, err := k.St.UserByID(ctx, link.UserID)
+		return u, link, err
+	case !errors.Is(err, store.ErrNotFound):
+		return store.User{}, link, err
+	}
+	email := store.NormalizeEmail(id.Email)
+	if email == "" {
+		return store.User{}, link, ErrNoEmail
+	}
+	u, err := k.St.UserByEmail(ctx, email)
+	switch {
+	case errors.Is(err, store.ErrNotFound) && k.CreateAccounts:
+		name := id.Name
+		if name == "" {
+			name = email
+		}
+		u = store.User{ID: "usr-" + randomID(), Email: email, Name: name,
+			// No password works here: the directory's is checked.
+			PasswordHash: "!" + k.Name, State: store.UserActive, CreatedAt: k.now()}
+		if err := k.St.CreateUser(ctx, u); err != nil {
+			return store.User{}, link, err
+		}
+	case errors.Is(err, store.ErrNotFound):
+		return store.User{}, link, fmt.Errorf("%w: %s", ErrNoAccount, email)
+	case err != nil:
+		return store.User{}, link, err
+	}
+	if err := k.St.LinkDirectory(ctx, u.ID, k.Name, id.ID, k.now()); err != nil {
+		return store.User{}, link, err
+	}
+	return u, store.DirectoryLink{UserID: u.ID, Directory: k.Name, ExternalID: id.ID}, nil
+}
+
+// apply gives the account the role and places its groups map to. With
+// remove, a place this directory gave that the groups no longer do is taken
+// away; one given otherwise is never touched.
+func (k *Keeper) apply(ctx context.Context, u *store.User, id Identity, remove bool) error {
+	if len(k.Mapping.Roles) > 0 {
+		if role := k.Mapping.Role(id.Groups); role != u.StaffRole() {
+			if err := k.St.SetStaffRole(ctx, u.ID, role); err != nil {
+				return err
+			}
+			u.IsAdmin, u.Role = role == store.RoleAdmin, role
+			if role == store.RoleAdmin {
+				u.Role = ""
+			}
+		}
+	}
+	want := map[string]store.Scope{}
+	for _, where := range k.Mapping.Places(id.Groups) {
+		scope, sid, err := k.place(ctx, where)
+		if err != nil {
+			continue // a mapping to a place the tree lacks: said by Sync
+		}
+		want[string(scope)+"/"+sid] = scope
+		if err := k.St.AddMembership(ctx, u.ID, scope, sid, store.RoleMember, k.Name, k.now()); err != nil {
+			return err
+		}
+	}
+	if !remove {
+		return nil
+	}
+	have, err := k.St.MembershipsOf(ctx, u.ID)
+	if err != nil {
+		return err
+	}
+	for _, m := range have {
+		if m.AddedBy != k.Name {
+			continue
+		}
+		if _, ok := want[string(m.Scope)+"/"+m.ScopeID]; ok {
+			continue
+		}
+		if _, err := k.St.RemoveMembership(ctx, u.ID, m.Scope, m.ScopeID, k.now()); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (k *Keeper) reinstate(ctx context.Context, u store.User) (store.User, error) {
+	if err := k.St.SetUserState(ctx, u.ID, store.UserActive); err != nil {
+		return u, err
+	}
+	if err := k.St.SetSyncSuspended(ctx, u.ID, false, k.now()); err != nil {
+		return u, err
+	}
+	u.State = store.UserActive
+	return u, nil
+}
+
+// SyncReport is what a sync did.
+type SyncReport struct {
+	Seen, Updated, Suspended, Reinstated int
+	// Unmapped are mappings to places the tree does not have.
+	Unmapped []string
+}
+
+// Sync brings every account the directory keeps in step with what it says
+// now: people disabled or gone there are suspended here (their sessions
+// ended; their keys refuse, as a suspended owner's do), those enabled again
+// that the sync had suspended are reinstated, and everyone's role and places
+// follow their groups. People the directory has that never signed in here
+// are left until they do.
+func (k *Keeper) Sync(ctx context.Context, people []Identity) (SyncReport, error) {
+	var rep SyncReport
+	rep.Unmapped = k.unmapped(ctx)
+	byID := make(map[string]Identity, len(people))
+	for _, p := range people {
+		byID[p.ID] = p
+	}
+	links, err := k.St.DirectoryLinks(ctx, k.Name)
+	if err != nil {
+		return rep, err
+	}
+	// A directory that answers with nobody, or with half the people missing,
+	// is far likelier a wrong base, a filter or a bind account's lost rights
+	// than half the company leaving at once. Nothing is suspended for it.
+	gone := 0
+	for _, l := range links {
+		if p, there := byID[l.ExternalID]; !there || p.Disabled {
+			gone++
+		}
+	}
+	if len(links) > 0 && (len(people) == 0 || (gone >= 3 && gone*2 > len(links))) {
+		return rep, fmt.Errorf("%w: %d of the %d accounts it keeps would be suspended", ErrImplausible, gone, len(links))
+	}
+	for _, l := range links {
+		rep.Seen++
+		u, err := k.St.UserByID(ctx, l.UserID)
+		if err != nil {
+			continue
+		}
+		p, there := byID[l.ExternalID]
+		switch {
+		case !there || p.Disabled:
+			if u.State == store.UserActive {
+				if err := k.St.SetUserState(ctx, u.ID, store.UserSuspended); err != nil {
+					return rep, err
+				}
+				if err := k.St.DeleteUserSessions(ctx, u.ID); err != nil {
+					return rep, err
+				}
+				if err := k.St.SetSyncSuspended(ctx, u.ID, true, k.now()); err != nil {
+					return rep, err
+				}
+				rep.Suspended++
+			}
+		default:
+			if u.State == store.UserSuspended && l.SuspendedBySync {
+				if u, err = k.reinstate(ctx, u); err != nil {
+					return rep, err
+				}
+				rep.Reinstated++
+			}
+			if u.State != store.UserActive {
+				continue
+			}
+			before := u.StaffRole()
+			if err := k.apply(ctx, &u, p, true); err != nil {
+				return rep, err
+			}
+			if u.StaffRole() != before {
+				rep.Updated++
+			}
+		}
+	}
+	return rep, nil
+}
+
+// unmapped are the mapping's places the tree does not have.
+func (k *Keeper) unmapped(ctx context.Context) []string {
+	var out []string
+	for _, where := range k.Mapping.Memberships {
+		if _, _, err := k.place(ctx, where); err != nil && !slices.Contains(out, where) {
+			out = append(out, where)
+		}
+	}
+	slices.Sort(out)
+	return out
+}
+
+// place finds org:NAME, team:ORG/TEAM, project:ORG/TEAM/PROJECT, as
+// auth.oidc's mapping does.
+func (k *Keeper) place(ctx context.Context, where string) (store.Scope, string, error) {
+	kind, path, _ := strings.Cut(where, ":")
+	norm := func(s string) string {
+		parts := strings.Split(s, "/")
+		for i := range parts {
+			parts[i] = strings.TrimSpace(parts[i])
+		}
+		return strings.Join(parts, "/")
+	}
+	same := func(a string) bool { return strings.EqualFold(norm(a), norm(path)) }
+	switch kind {
+	case "org":
+		orgs, err := k.St.AllOrgs(ctx)
+		for _, o := range orgs {
+			if same(o.Name) {
+				return store.ScopeOrg, o.ID, nil
+			}
+		}
+		return "", "", errors.Join(err, errors.New("no such organization"))
+	case "team":
+		teams, err := k.St.AllTeams(ctx)
+		for _, t := range teams {
+			if same(t.OrgName + "/" + t.Name) {
+				return store.ScopeTeam, t.ID, nil
+			}
+		}
+		return "", "", errors.Join(err, errors.New("no such team"))
+	default:
+		projects, err := k.St.AllProjects(ctx)
+		for _, p := range projects {
+			if same(p.Path) {
+				return store.ScopeProject, p.ID, nil
+			}
+		}
+		return "", "", errors.Join(err, errors.New("no such project"))
+	}
+}
+
+func randomID() string {
+	var b [8]byte
+	_, _ = rand.Read(b[:])
+	return hex.EncodeToString(b[:])
+}
diff --git a/internal/directory/directory_test.go b/internal/directory/directory_test.go
new file mode 100644
index 0000000..2174c79
--- /dev/null
+++ b/internal/directory/directory_test.go
@@ -0,0 +1,142 @@
+package directory
+
+import (
+	"errors"
+	"path/filepath"
+	"slices"
+	"testing"
+	"time"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/store"
+)
+
+func newKeeper(t *testing.T) (*Keeper, *store.DB, string) {
+	t.Helper()
+	st, err := store.Open(t.Context(), filepath.Join(t.TempDir(), "s.db"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { st.Close() })
+	org, _ := st.CreateOrg(t.Context(), "Acme")
+	team, _ := st.CreateTeam(t.Context(), org, "ml")
+	k := &Keeper{St: st, Name: "ldap", CreateAccounts: true, Mapping: Mapping{
+		Roles:       map[string][]string{"admin": {"llmgw-admins"}, "viewer": {"CN=Staff,OU=Groups,DC=corp,DC=example"}},
+		Memberships: map[string]string{"ml-team": "team:Acme/ml", "ghosts": "team:Acme/nowhere"},
+	}}
+	return k, st, team
+}
+
+var ada = Identity{ID: "guid-ada", DN: "CN=Ada,OU=Staff,DC=corp,DC=example", Email: "Ada@Corp.example", Name: "Ada L",
+	Groups: []string{"ml-team", "CN=ml-team,OU=Groups,DC=corp,DC=example", "Staff", "CN=Staff,OU=Groups,DC=corp,DC=example"}}
+
+func TestAPersonTheDirectoryVouchesForIsMadeAnAccountWithWhatTheirGroupsGive(t *testing.T) {
+	k, st, team := newKeeper(t)
+	u, err := k.SignIn(t.Context(), ada)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if u.Email != "ada@corp.example" || u.Name != "Ada L" || u.PasswordHash != "!ldap" || u.StaffRole() != "viewer" {
+		t.Errorf("account %+v role %q", u, u.StaffRole())
+	}
+	ms, _ := st.MembershipsOf(t.Context(), u.ID)
+	if len(ms) != 1 || ms[0].ScopeID != team || ms[0].AddedBy != "ldap" {
+		t.Errorf("memberships %+v", ms)
+	}
+	// Their mail changes there: still the same account, by its directory id.
+	moved := ada
+	moved.Email = "ada.lovelace@corp.example"
+	again, err := k.SignIn(t.Context(), moved)
+	if err != nil || again.ID != u.ID {
+		t.Errorf("a new mail made a new account: %v %+v", err, again)
+	}
+	// The higher role of two wins.
+	boss := ada
+	boss.Groups = append(slices.Clone(ada.Groups), "llmgw-admins")
+	if u, _ := k.SignIn(t.Context(), boss); u.StaffRole() != "admin" {
+		t.Errorf("role %q", u.StaffRole())
+	}
+}
+
+func TestWithoutAccountsMadeOnlyThoseThatExistSignIn(t *testing.T) {
+	k, _, _ := newKeeper(t)
+	k.CreateAccounts = false
+	if _, err := k.SignIn(t.Context(), ada); !errors.Is(err, ErrNoAccount) {
+		t.Errorf("err %v", err)
+	}
+}
+
+func TestTheSyncSuspendsWhomTheDirectoryDisabledAndReinstatesThemAfter(t *testing.T) {
+	k, st, _ := newKeeper(t)
+	ctx := t.Context()
+	people := []Identity{ada}
+	for _, n := range []string{"b", "c", "d"} {
+		people = append(people, Identity{ID: "guid-" + n, Email: n + "@corp.example"})
+	}
+	ids := map[string]string{}
+	for _, p := range people {
+		u, err := k.SignIn(ctx, p)
+		if err != nil {
+			t.Fatal(err)
+		}
+		ids[p.ID] = u.ID
+	}
+	if err := st.CreateSession(ctx, ids["guid-ada"], "tok", "csrf", time.Hour); err != nil {
+		t.Fatal(err)
+	}
+	// An administrator suspends c here, by hand.
+	_ = st.SetUserState(ctx, ids["guid-c"], store.UserSuspended)
+
+	// Ada is disabled there, and has left ml-team.
+	off := ada
+	off.Disabled = true
+	rep, err := k.Sync(ctx, []Identity{off, people[1], people[2], people[3]})
+	if err != nil {
+		t.Fatal(err)
+	}
+	u, _ := st.UserByID(ctx, ids["guid-ada"])
+	if u.State != store.UserSuspended || rep.Suspended != 1 {
+		t.Errorf("ada %s, report %+v", u.State, rep)
+	}
+	if _, _, err := st.SessionByToken(ctx, "tok"); err == nil {
+		t.Error("a suspended account's session still works")
+	}
+	if !slices.Contains(rep.Unmapped, "team:Acme/nowhere") {
+		t.Errorf("an unmapped place was not said: %+v", rep)
+	}
+
+	// Enabled again, and out of ml-team: reinstated, and its place taken
+	// away. c, suspended by hand, stays so.
+	back := ada
+	back.Groups = []string{"Staff", "CN=Staff,OU=Groups,DC=corp,DC=example"}
+	rep, err = k.Sync(ctx, []Identity{back, people[1], people[2], people[3]})
+	if err != nil {
+		t.Fatal(err)
+	}
+	u, _ = st.UserByID(ctx, ids["guid-ada"])
+	ms, _ := st.MembershipsOf(ctx, u.ID)
+	if u.State != store.UserActive || rep.Reinstated != 1 || len(ms) != 0 {
+		t.Errorf("ada %s, memberships %+v, report %+v", u.State, ms, rep)
+	}
+	if c, _ := st.UserByID(ctx, ids["guid-c"]); c.State != store.UserSuspended {
+		t.Errorf("an account suspended by hand was reinstated: %s", c.State)
+	}
+}
+
+func TestASyncThatWouldSuspendMostIsRefused(t *testing.T) {
+	k, st, _ := newKeeper(t)
+	ctx := t.Context()
+	for _, n := range []string{"a", "b", "c", "d"} {
+		if _, err := k.SignIn(ctx, Identity{ID: "guid-" + n, Email: n + "@corp.example"}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, people := range [][]Identity{nil, {{ID: "guid-a", Email: "a@corp.example"}}} {
+		if _, err := k.Sync(ctx, people); !errors.Is(err, ErrImplausible) {
+			t.Errorf("%d people: %v", len(people), err)
+		}
+	}
+	users, _ := st.Users(ctx, store.UserSuspended)
+	if len(users) != 0 {
+		t.Errorf("suspended %d", len(users))
+	}
+}
diff --git a/internal/directory/ldap.go b/internal/directory/ldap.go
new file mode 100644
index 0000000..e522e48
--- /dev/null
+++ b/internal/directory/ldap.go
@@ -0,0 +1,286 @@
+package directory
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/go-ldap/ldap/v3"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/config"
+	"gitea.mynodes.xyz/ilker/llmgw/internal/secrets"
+)
+
+// LDAP is a directory reached over LDAP, written for Active Directory: its
+// attribute names, its disabled flag, and its matching rule for nested
+// groups (LDAP_MATCHING_RULE_IN_CHAIN).
+type LDAP struct {
+	cfg  config.LDAP
+	tls  *tls.Config
+	dial func(url string) (ldapConn, error)
+}
+
+// ldapConn is the part of a connection used here, so tests need no server.
+type ldapConn interface {
+	Bind(user, password string) error
+	Search(*ldap.SearchRequest) (*ldap.SearchResult, error)
+	SearchWithPaging(*ldap.SearchRequest, uint32) (*ldap.SearchResult, error)
+	Close() error
+}
+
+// inChain is AD's matching rule that follows nested group membership.
+const inChain = "1.2.840.113556.1.4.1941"
+
+// uacDisabled is userAccountControl's ACCOUNTDISABLE bit.
+const uacDisabled = 0x2
+
+var personAttrs = []string{"objectGUID", "sAMAccountName", "userPrincipalName", "mail", "displayName", "userAccountControl"}
+
+// ErrBadCredentials is a person the directory does not know, or a password
+// it does not take: said alike, so a form cannot tell which.
+var ErrBadCredentials = errors.New("the directory does not take that name and password")
+
+// NewLDAP prepares a directory from its configuration.
+func NewLDAP(cfg config.LDAP) (*LDAP, error) {
+	tc := &tls.Config{MinVersion: tls.VersionTLS12}
+	if cfg.CAFile != "" {
+		pem, err := os.ReadFile(cfg.CAFile)
+		if err != nil {
+			return nil, fmt.Errorf("auth.ldap.ca_file: %w", err)
+		}
+		pool := x509.NewCertPool()
+		if !pool.AppendCertsFromPEM(pem) {
+			return nil, fmt.Errorf("auth.ldap.ca_file %s holds no certificate", cfg.CAFile)
+		}
+		tc.RootCAs = pool
+	}
+	d := &LDAP{cfg: cfg, tls: tc}
+	d.dial = d.dialURL
+	return d, nil
+}
+
+func (d *LDAP) dialURL(u string) (ldapConn, error) {
+	c, err := ldap.DialURL(u, ldap.DialWithTLSConfig(d.tls))
+	if err != nil {
+		return nil, err
+	}
+	c.SetTimeout(d.cfg.RoundTrip())
+	if strings.HasPrefix(u, "ldap://") {
+		// Validate refuses ldap:// without start_tls: nothing is sent first.
+		if err := c.StartTLS(d.tls); err != nil {
+			c.Close()
+			return nil, fmt.Errorf("StartTLS: %w", err)
+		}
+	}
+	return c, nil
+}
+
+// service is a connection bound as the account that finds people, to the
+// first server that answers.
+func (d *LDAP) service(ctx context.Context) (ldapConn, error) {
+	pw, err := secrets.Read(ctx, d.cfg.BindPasswordFile)
+	if err != nil {
+		return nil, fmt.Errorf("auth.ldap.bind_password_file: %w", err)
+	}
+	var errs []error
+	for _, u := range d.cfg.URLs {
+		c, err := d.dial(u)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("%s: %w", u, err))
+			continue
+		}
+		if err := c.Bind(d.cfg.BindDN, strings.TrimSpace(string(pw))); err != nil {
+			c.Close()
+			// A server that refuses the service account refuses it
+			// everywhere: not tried on the next.
+			return nil, fmt.Errorf("binding as %s on %s: %w", d.cfg.BindDN, u, err)
+		}
+		return c, nil
+	}
+	return nil, fmt.Errorf("no directory server answered: %w", errors.Join(errs...))
+}
+
+// Authenticate checks a person's name and password against the directory
+// and says who they are there, groups and all.
+func (d *LDAP) Authenticate(ctx context.Context, login, password string) (Identity, error) {
+	login = strings.TrimSpace(login)
+	// An empty password is an unauthenticated bind, which succeeds: never
+	// one for a person.
+	if login == "" || password == "" {
+		return Identity{}, ErrBadCredentials
+	}
+	// DOMAIN\user, as Windows writes it.
+	if i := strings.LastIndexByte(login, '\\'); i >= 0 {
+		login = login[i+1:]
+	}
+	c, err := d.service(ctx)
+	if err != nil {
+		return Identity{}, err
+	}
+	defer c.Close()
+	q := ldap.EscapeFilter(login)
+	filter := "(&" + d.people(false) + "(|(sAMAccountName=" + q + ")(userPrincipalName=" + q + ")(mail=" + q + ")))"
+	res, err := c.Search(ldap.NewSearchRequest(d.cfg.BaseDN, ldap.ScopeWholeSubtree, ldap.NeverDerefAliases,
+		2, 0, false, filter, personAttrs, nil))
+	if err != nil {
+		return Identity{}, fmt.Errorf("finding %s: %w", login, err)
+	}
+	if len(res.Entries) != 1 {
+		// None, or two people one name matches: neither is let in.
+		return Identity{}, ErrBadCredentials
+	}
+	id := identity(res.Entries[0])
+	if err := c.Bind(id.DN, password); err != nil {
+		var le *ldap.Error
+		if errors.As(err, &le) && le.ResultCode == ldap.LDAPResultInvalidCredentials {
+			return Identity{}, ErrBadCredentials
+		}
+		return Identity{}, fmt.Errorf("checking %s's password: %w", login, err)
+	}
+	// Back to the service account to read groups, which a person may not.
+	pw, err := secrets.Read(ctx, d.cfg.BindPasswordFile)
+	if err != nil {
+		return Identity{}, err
+	}
+	if err := c.Bind(d.cfg.BindDN, strings.TrimSpace(string(pw))); err != nil {
+		return Identity{}, err
+	}
+	if id.Groups, err = d.groupsOf(c, id.DN); err != nil {
+		return Identity{}, err
+	}
+	return id, nil
+}
+
+// groupsOf are a person's groups, nested ones included, by CN and DN.
+func (d *LDAP) groupsOf(c ldapConn, dn string) ([]string, error) {
+	filter := "(&(objectClass=group)(member:" + inChain + ":=" + ldap.EscapeFilter(dn) + "))"
+	res, err := c.SearchWithPaging(ldap.NewSearchRequest(d.groupBase(), ldap.ScopeWholeSubtree, ldap.NeverDerefAliases,
+		0, 0, false, filter, []string{"cn"}, nil), 500)
+	if err != nil {
+		return nil, fmt.Errorf("reading the groups of %s: %w", dn, err)
+	}
+	var out []string
+	for _, e := range res.Entries {
+		out = append(out, e.GetAttributeValue("cn"), e.DN)
+	}
+	return out, nil
+}
+
+// People are everyone the directory has under the base, enabled or not,
+// each with the mapped groups they are in: what a sync compares against.
+func (d *LDAP) People(ctx context.Context, m Mapping) ([]Identity, error) {
+	c, err := d.service(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer c.Close()
+	res, err := c.SearchWithPaging(ldap.NewSearchRequest(d.cfg.BaseDN, ldap.ScopeWholeSubtree, ldap.NeverDerefAliases,
+		0, 0, false, d.people(true), personAttrs, nil), 500)
+	if err != nil {
+		return nil, fmt.Errorf("listing people: %w", err)
+	}
+	people := make([]Identity, 0, len(res.Entries))
+	at := map[string]int{}
+	for _, e := range res.Entries {
+		id := identity(e)
+		at[id.ID] = len(people)
+		people = append(people, id)
+	}
+	// Only the groups the mapping names matter: a query each, for its
+	// members nested ones included, rather than one per person.
+	for _, g := range m.Groups() {
+		dns, err := d.groupDNs(c, g)
+		if err != nil {
+			return nil, err
+		}
+		for _, gdn := range dns {
+			filter := "(&" + d.people(true) + "(memberOf:" + inChain + ":=" + ldap.EscapeFilter(gdn) + "))"
+			r, err := c.SearchWithPaging(ldap.NewSearchRequest(d.cfg.BaseDN, ldap.ScopeWholeSubtree,
+				ldap.NeverDerefAliases, 0, 0, false, filter, []string{"objectGUID"}, nil), 500)
+			if err != nil {
+				return nil, fmt.Errorf("reading the members of %s: %w", gdn, err)
+			}
+			for _, e := range r.Entries {
+				if i, ok := at[guid(e.GetRawAttributeValue("objectGUID"))]; ok {
+					people[i].Groups = append(people[i].Groups, g, gdn)
+				}
+			}
+		}
+	}
+	return people, nil
+}
+
+// groupDNs are the groups a mapping's name means: a DN as it is, a CN
+// looked up.
+func (d *LDAP) groupDNs(c ldapConn, g string) ([]string, error) {
+	if strings.Contains(g, "=") {
+		return []string{g}, nil
+	}
+	res, err := c.Search(ldap.NewSearchRequest(d.groupBase(), ldap.ScopeWholeSubtree, ldap.NeverDerefAliases,
+		0, 0, false, "(&(objectClass=group)(cn="+ldap.EscapeFilter(g)+"))", []string{"cn"}, nil))
+	if err != nil {
+		return nil, fmt.Errorf("finding the group %s: %w", g, err)
+	}
+	var out []string
+	for _, e := range res.Entries {
+		out = append(out, e.DN)
+	}
+	return out, nil
+}
+
+// people is the filter for person accounts under the user filter; enabled
+// ones only, unless all.
+func (d *LDAP) people(all bool) string {
+	f := "(objectCategory=person)(objectClass=user)"
+	if !all {
+		f += "(!(userAccountControl:1.2.840.113556.1.4.803:=" + strconv.Itoa(uacDisabled) + "))"
+	}
+	return "(&" + f + d.cfg.UserFilter + ")"
+}
+
+// groupBase is where groups are searched: GroupBaseDN, else the domain root
+// of BaseDN (its DC= parts).
+func (d *LDAP) groupBase() string {
+	if d.cfg.GroupBaseDN != "" {
+		return d.cfg.GroupBaseDN
+	}
+	var dc []string
+	for _, rdn := range strings.Split(d.cfg.BaseDN, ",") {
+		if strings.HasPrefix(strings.ToUpper(strings.TrimSpace(rdn)), "DC=") {
+			dc = append(dc, strings.TrimSpace(rdn))
+		}
+	}
+	if len(dc) == 0 {
+		return d.cfg.BaseDN
+	}
+	return strings.Join(dc, ",")
+}
+
+func identity(e *ldap.Entry) Identity {
+	email := e.GetAttributeValue("mail")
+	if email == "" {
+		email = e.GetAttributeValue("userPrincipalName")
+	}
+	uac, _ := strconv.Atoi(e.GetAttributeValue("userAccountControl"))
+	return Identity{
+		ID: guid(e.GetRawAttributeValue("objectGUID")), DN: e.DN,
+		Email: email, Name: e.GetAttributeValue("displayName"),
+		Disabled: uac&uacDisabled != 0,
+	}
+}
+
+// guid is an objectGUID as Windows writes it: its first three parts
+// little-endian. Another directory's id is kept as hex.
+func guid(b []byte) string {
+	if len(b) != 16 {
+		return fmt.Sprintf("%x", b)
+	}
+	return fmt.Sprintf("%08x-%04x-%04x-%x-%x", binary.LittleEndian.Uint32(b[0:4]),
+		binary.LittleEndian.Uint16(b[4:6]), binary.LittleEndian.Uint16(b[6:8]), b[8:10], b[10:16])
+}
diff --git a/internal/directory/ldap_test.go b/internal/directory/ldap_test.go
new file mode 100644
index 0000000..625b661
--- /dev/null
+++ b/internal/directory/ldap_test.go
@@ -0,0 +1,130 @@
+package directory
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/go-ldap/ldap/v3"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/config"
+)
+
+// fakeConn is a directory with one person in it.
+type fakeConn struct {
+	binds    []string
+	filters  []string
+	password string // the person's
+	people   int    // how many the person search finds
+}
+
+func (f *fakeConn) Bind(user, password string) error {
+	f.binds = append(f.binds, user)
+	if strings.HasPrefix(user, "CN=Ada") && password != f.password {
+		return &ldap.Error{ResultCode: ldap.LDAPResultInvalidCredentials}
+	}
+	return nil
+}
+
+func (f *fakeConn) Search(r *ldap.SearchRequest) (*ldap.SearchResult, error) {
+	f.filters = append(f.filters, r.Filter)
+	var out []*ldap.Entry
+	for i := range f.people {
+		e := ldap.NewEntry("CN=Ada,OU=Staff,DC=corp,DC=example", map[string][]string{
+			"mail": {"ada@corp.example"}, "displayName": {"Ada"}, "userAccountControl": {"512"},
+		})
+		e.Attributes = append(e.Attributes, &ldap.EntryAttribute{Name: "objectGUID", ByteValues: [][]byte{guidBytes(byte(i))}})
+		out = append(out, e)
+	}
+	return &ldap.SearchResult{Entries: out}, nil
+}
+
+func (f *fakeConn) SearchWithPaging(r *ldap.SearchRequest, _ uint32) (*ldap.SearchResult, error) {
+	f.filters = append(f.filters, r.Filter)
+	return &ldap.SearchResult{Entries: []*ldap.Entry{
+		ldap.NewEntry("CN=ml-team,OU=Groups,DC=corp,DC=example", map[string][]string{"cn": {"ml-team"}}),
+	}}, nil
+}
+
+func (f *fakeConn) Close() error { return nil }
+
+func guidBytes(last byte) []byte {
+	return []byte{0x78, 0x56, 0x34, 0x12, 0x34, 0x12, 0x78, 0x56, 0x9a, 0xbc, 0xde, 0xf0, 0x12, 0x34, 0x56, last}
+}
+
+func fakeLDAP(t *testing.T, c *fakeConn) *LDAP {
+	t.Helper()
+	pw := filepath.Join(t.TempDir(), "bind")
+	_ = os.WriteFile(pw, []byte("svc-secret\n"), 0o600)
+	d, err := NewLDAP(config.LDAP{URLs: []string{"ldaps://dc1"}, BindDN: "CN=llmgw,OU=Svc,DC=corp,DC=example",
+		BindPasswordFile: pw, BaseDN: "OU=Staff,DC=corp,DC=example", UserFilter: "(memberOf=CN=llm,DC=corp,DC=example)"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	d.dial = func(string) (ldapConn, error) { return c, nil }
+	return d
+}
+
+func TestAPersonIsCheckedByBindingAsThemAndTheirGroupsReadNested(t *testing.T) {
+	c := &fakeConn{password: "ad-secret", people: 1}
+	d := fakeLDAP(t, c)
+	id, err := d.Authenticate(t.Context(), `CORP\ada*)(x=`, "ad-secret")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id.Email != "ada@corp.example" || id.ID != "12345678-1234-5678-9abc-def012345600" ||
+		!slicesHas(id.Groups, "ml-team") || !slicesHas(id.Groups, "CN=ml-team,OU=Groups,DC=corp,DC=example") {
+		t.Errorf("identity %+v", id)
+	}
+	// The name is escaped into the filter, the domain part dropped; the
+	// user filter is ANDed in; disabled accounts are not found; groups are
+	// read with the in-chain rule.
+	find, groups := c.filters[0], c.filters[1]
+	if !strings.Contains(find, `(sAMAccountName=ada\2a\29\28x=)`) || !strings.Contains(find, "(memberOf=CN=llm,DC=corp,DC=example)") ||
+		!strings.Contains(find, "1.2.840.113556.1.4.803:=2") || !strings.Contains(groups, inChain) {
+		t.Errorf("filters %q", c.filters)
+	}
+	// Service account, then the person, then the service account again.
+	if len(c.binds) != 3 || c.binds[1] != "CN=Ada,OU=Staff,DC=corp,DC=example" {
+		t.Errorf("binds %v", c.binds)
+	}
+}
+
+func TestWrongPasswordsEmptyOnesAndAmbiguousNamesAreRefusedAlike(t *testing.T) {
+	for _, tc := range []struct {
+		people   int
+		password string
+	}{{1, "wrong"}, {1, ""}, {0, "ad-secret"}, {2, "ad-secret"}} {
+		d := fakeLDAP(t, &fakeConn{password: "ad-secret", people: tc.people})
+		if _, err := d.Authenticate(t.Context(), "ada", tc.password); !errors.Is(err, ErrBadCredentials) {
+			t.Errorf("%d found, password %q: %v", tc.people, tc.password, err)
+		}
+	}
+}
+
+func TestPlaintextLDAPIsRefusedWithoutStartTLS(t *testing.T) {
+	base := config.LDAP{BindDN: "CN=x", BindPasswordFile: "/f", BaseDN: "DC=corp"}
+	for _, c := range []struct {
+		urls  []string
+		start bool
+		ok    bool
+	}{{[]string{"ldaps://dc1"}, false, true}, {[]string{"ldap://dc1"}, false, false},
+		{[]string{"ldap://dc1"}, true, true}, {[]string{"http://dc1"}, true, false}} {
+		l := base
+		l.URLs, l.StartTLS = c.urls, c.start
+		if err := l.Validate(); (err == nil) != c.ok {
+			t.Errorf("%v start_tls=%v: %v", c.urls, c.start, err)
+		}
+	}
+}
+
+func slicesHas(xs []string, x string) bool {
+	for _, v := range xs {
+		if v == x {
+			return true
+		}
+	}
+	return false
+}
diff --git a/internal/docgen/reference_gen.go b/internal/docgen/reference_gen.go
index 6d2ffb5..f97cdaf 100644
--- a/internal/docgen/reference_gen.go
+++ b/internal/docgen/reference_gen.go
@@ -33,6 +33,7 @@ var Reference = []Block{
 		{Key: "default_tpm", Type: "int", Doc: "", Nested: ""},
 		{Key: "signup_open", Type: "bool", Doc: "SignupOpen serves the signup form. Accounts it creates are pending until\nan operator approves them, so this is not a way in — but turning it off\nmeans accounts are made with `llmgw users create` instead.", Nested: ""},
 		{Key: "oidc", Type: "OIDC", Doc: "OIDC is sign-in through an identity provider.", Nested: "config.OIDC"},
+		{Key: "ldap", Type: "LDAP", Doc: "LDAP is sign-in against a directory, Active Directory above all, and\nthe accounts kept in step with it.", Nested: "config.LDAP"},
 		{Key: "scim", Type: "SCIM", Doc: "SCIM is account provisioning by the identity provider.", Nested: "config.SCIM"},
 		{Key: "max_key_ttl", Type: "time.Duration", Doc: "MaxKeyTTL is how long any API key may live; a key asked for with no\nexpiry is given this. Organizations, teams and projects can set\nshorter ones (llmgw keys ttl). Zero is no limit.", Nested: ""},
 		{Key: "personal", Type: "Personal", Doc: "Personal is what a person may do on their own, outside any project: make\npersonal keys and use the chat page personally, within these limits.", Nested: "config.Personal"},
@@ -188,6 +189,22 @@ var Reference = []Block{
 		{Key: "min_blocks", Type: "int", Doc: "MinBlocks is the fewest leading blocks a replica must hold to be\npreferred for them; fewer is coincidence — a chat template's opening\ntokens — rather than a prefix worth following. Zero takes 4, which is\n64 tokens at vLLM's usual block size of 16.", Nested: ""},
 		{Key: "max_blocks", Type: "int", Doc: "MaxBlocks bounds how many of a prompt's blocks are hashed and looked\nup. Beyond it a longer match still helps, but the difference no longer\ndecides anything. Zero takes 4096.", Nested: ""},
 	}},
+	{Package: "config", Name: "LDAP", Title: "LDAP", Doc: "", Fields: []Field{
+		{Key: "urls", Type: "[]string", Doc: "URLs are the directory's servers, tried in turn: ldaps:// (636), or\nldap:// (389) with StartTLS.", Nested: ""},
+		{Key: "start_tls", Type: "bool", Doc: "StartTLS upgrades an ldap:// connection before anything is sent. A\npassword never crosses a connection without TLS: ldap:// without it\nis refused.", Nested: ""},
+		{Key: "ca_file", Type: "string", Doc: "CAFile is the authority the servers' certificates are checked against,\nwhen it is not the system's: an AD Certificate Services root.", Nested: ""},
+		{Key: "bind_dn", Type: "string", Doc: "BindDN and the file holding its password: a service account that may\nread users and groups. Nothing is written to the directory.", Nested: ""},
+		{Key: "bind_password_file", Type: "string", Doc: "", Nested: ""},
+		{Key: "base_dn", Type: "string", Doc: "BaseDN is where people are searched for, subtree included.", Nested: ""},
+		{Key: "group_base_dn", Type: "string", Doc: "GroupBaseDN is where their groups are; empty is BaseDN's domain root.", Nested: ""},
+		{Key: "user_filter", Type: "string", Doc: "UserFilter narrows who may sign in, ANDed with the login match: a\ngroup (memberOf=...) or an OU's people only. Empty is every enabled\nuser object.", Nested: ""},
+		{Key: "label", Type: "string", Doc: "Label is what the form says to sign in with: \"Sign in with your\n<label> account\". Empty is \"Active Directory\".", Nested: ""},
+		{Key: "create_accounts", Type: "bool", Doc: "CreateAccounts makes an account, active, for a person the directory\nvouches for and the gateway does not know. Off, only existing accounts\nsign in this way.", Nested: ""},
+		{Key: "roles", Type: "map[string][]string", Doc: "Roles maps a staff role (viewer, operator, billing, admin) to the\ngroups that give it, by name (CN) or whole DN. Set at every sign-in\nand sync: someone taken out of the group loses the role.", Nested: ""},
+		{Key: "memberships", Type: "map[string]string", Doc: "Memberships maps a group, by CN or DN, to a place in the tree —\norg:NAME, team:ORG/TEAM, project:ORG/TEAM/PROJECT — joined at sign-in\nand kept by the sync, which also takes away a place whose group the\nperson has left.", Nested: ""},
+		{Key: "sync_interval", Type: "time.Duration", Doc: "SyncInterval is how often the leader reads the directory. Zero is\n15m; negative turns the sync off, leaving only sign-in.", Nested: ""},
+		{Key: "timeout", Type: "time.Duration", Doc: "Timeout bounds each round trip to a server. Zero is 10s.", Nested: ""},
+	}},
 	{Package: "config", Name: "Landing", Title: "Landing", Doc: "", Fields: []Field{
 		{Key: "contact", Type: "string", Doc: "Contact is where someone without a key should go — an address, a URL, a\nchannel name. Rendered as a link when it is one, as text otherwise.", Nested: ""},
 		{Key: "notice", Type: "string", Doc: "Notice is an optional line of your own, for whatever the reader needs to\nknow that this page cannot guess.", Nested: ""},
diff --git a/internal/docgen/render.go b/internal/docgen/render.go
index 500712e..82c0c9a 100644
--- a/internal/docgen/render.go
+++ b/internal/docgen/render.go
@@ -33,6 +33,7 @@ var Sources = []string{
 	"internal/guard/policy.go",
 	"internal/guard/judge.go",
 	"internal/config/oidc.go",
+	"internal/config/ldap.go",
 	"internal/config/firewall.go",
 	"internal/config/serving.go",
 	"internal/config/presets.go",
diff --git a/internal/router/directory.go b/internal/router/directory.go
new file mode 100644
index 0000000..2eea600
--- /dev/null
+++ b/internal/router/directory.go
@@ -0,0 +1,112 @@
+package router
+
+import (
+	"cmp"
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"time"
+
+	"gitea.mynodes.xyz/ilker/llmgw/internal/account"
+	"gitea.mynodes.xyz/ilker/llmgw/internal/config"
+	"gitea.mynodes.xyz/ilker/llmgw/internal/directory"
+	storepkg "gitea.mynodes.xyz/ilker/llmgw/internal/store"
+)
+
+// Sign-in against a directory (auth.ldap), and the accounts kept in step
+// with it by the leader.
+
+// ldapDirectory is auth.ldap as the gateway uses it.
+type ldapDirectory struct {
+	dir    *directory.LDAP
+	keeper *directory.Keeper
+	every  time.Duration
+	label  string
+	log    *slog.Logger
+}
+
+func newLDAPDirectory(cfg config.LDAP, st *storepkg.DB, log *slog.Logger) (*ldapDirectory, error) {
+	dir, err := directory.NewLDAP(cfg)
+	if err != nil {
+		return nil, err
+	}
+	return &ldapDirectory{
+		dir: dir,
+		keeper: &directory.Keeper{St: st, Name: "ldap", CreateAccounts: cfg.CreateAccounts,
+			Mapping: directory.Mapping{Roles: cfg.Roles, Memberships: cfg.Memberships}},
+		every: cfg.Interval(),
+		label: cmp.Or(cfg.Label, "Active Directory"),
+		log:   log,
+	}, nil
+}
+
+// SignIn is account.Directory: the person's name and password checked by
+// the directory, then their account made or kept in step.
+func (d *ldapDirectory) SignIn(ctx context.Context, login, password string) (storepkg.User, error) {
+	id, err := d.dir.Authenticate(ctx, login, password)
+	switch {
+	case errors.Is(err, directory.ErrBadCredentials):
+		return storepkg.User{}, account.ErrBadCredentials
+	case err != nil:
+		d.log.Warn("the directory could not be asked about a sign-in", "err", err)
+		return storepkg.User{}, fmt.Errorf("the directory could not be asked: %w", err)
+	}
+	u, err := d.keeper.SignIn(ctx, id)
+	switch {
+	case errors.Is(err, directory.ErrSuspended):
+		return storepkg.User{}, account.ErrSuspended
+	case errors.Is(err, directory.ErrNoAccount), errors.Is(err, directory.ErrNoEmail):
+		// Said to the log, not the form: the form says what a wrong
+		// password says.
+		d.log.Info("the directory vouched for a person who has no account here", "dn", id.DN, "err", err)
+		return storepkg.User{}, account.ErrBadCredentials
+	case errors.Is(err, directory.ErrNotActive):
+		return storepkg.User{}, account.ErrNotApproved
+	case err != nil:
+		return storepkg.User{}, err
+	}
+	return u, nil
+}
+
+// sync reads the directory every interval, on the leader, and brings the
+// accounts it keeps in step.
+func (d *ldapDirectory) sync(ctx context.Context, leader func() bool) {
+	if d.every <= 0 {
+		return
+	}
+	t := time.NewTicker(d.every)
+	defer t.Stop()
+	for {
+		if leader() {
+			d.syncOnce(ctx)
+		}
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+		}
+	}
+}
+
+func (d *ldapDirectory) syncOnce(ctx context.Context) {
+	ctx, cancel := context.WithTimeout(ctx, 5*time.Minute)
+	defer cancel()
+	people, err := d.dir.People(ctx, d.keeper.Mapping)
+	if err != nil {
+		d.log.Warn("could not read the directory; accounts left as they are", "err", err)
+		return
+	}
+	rep, err := d.keeper.Sync(ctx, people)
+	if err != nil {
+		d.log.Error("the directory sync stopped", "err", err, "people", len(people))
+		return
+	}
+	for _, where := range rep.Unmapped {
+		d.log.Warn("auth.ldap.memberships maps a group to a place the tree does not have", "place", where)
+	}
+	if rep.Suspended+rep.Reinstated+rep.Updated > 0 {
+		d.log.Info("accounts kept in step with the directory", "people", len(people), "accounts", rep.Seen,
+			"suspended", rep.Suspended, "reinstated", rep.Reinstated, "roles_changed", rep.Updated)
+	}
+}
diff --git a/internal/router/handlers.go b/internal/router/handlers.go
index acdf2d7..ef2ba52 100644
--- a/internal/router/handlers.go
+++ b/internal/router/handlers.go
@@ -243,6 +243,9 @@ func (r *Router) Handler() http.Handler {
 			return web.ModelFacts{ContextLength: m.ContextLength, MaxOutput: m.MaxOutput, Tools: m.Capabilities.Tools}
 		})
 		pages.SetPersonalOff(r.personalOff)
+		if r.directory != nil {
+			pages.SetDirectory(r.directory.label)
+		}
 		pages.SetLlamaCppVersion(r.llamaVersion)
 		pages.SetPersonalDefaults(r.personalDefaults)
 		if r.store != nil {
diff --git a/internal/router/router.go b/internal/router/router.go
index 1acc3f8..a419c9a 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -119,6 +119,8 @@ type Router struct {
 	acct       *accounting.Accountant
 	// notifier says what the operator must act on; nil says nothing.
 	notifier *notify.Notifier
+	// directory is auth.ldap's: sign-in and the accounts kept in step.
+	directory *ldapDirectory
 	// guard judges requests and answers; nil judges nothing. guardLibrary
 	// is the policies it was built from, for the pages that show them.
 	guard        guard.Guard
@@ -395,6 +397,14 @@ func New(cfg config.Server, log *slog.Logger) (*Router, error) {
 		r.accounts = account.New(st, account.Config{
 			SignupOpen: cfg.Auth.SignupOpen,
 		}, log)
+		if cfg.Auth.LDAP.Enabled() {
+			d, err := newLDAPDirectory(cfg.Auth.LDAP, st, log)
+			if err != nil {
+				return nil, err
+			}
+			r.directory = d
+			r.accounts.SetDirectory(d)
+		}
 
 		r.acct = accounting.New(
 			accounting.NewPricing(prices, accounting.Price{
@@ -535,6 +545,9 @@ func (r *Router) Start(ctx context.Context) {
 	if r.threads != nil {
 		go r.pruneThreads(ctx)
 	}
+	if r.directory != nil {
+		go r.directory.sync(ctx, r.leading)
+	}
 	if r.store != nil && r.usageRetention > 0 {
 		go r.pruneUsage(ctx, r.usageRetention)
 	}
diff --git a/internal/store/copy.go b/internal/store/copy.go
index 93e8829..a9d0a9b 100644
--- a/internal/store/copy.go
+++ b/internal/store/copy.go
@@ -27,6 +27,8 @@ var copyOrder = []string{
 	"memberships",
 	// After users, which it points at.
 	"user_excluded_licences",
+	// After users, which it points at.
+	"user_directory",
 	"preset_state",
 	"api_keys",
 	"key_claims",
diff --git a/internal/store/directory.go b/internal/store/directory.go
new file mode 100644
index 0000000..dee50c7
--- /dev/null
+++ b/internal/store/directory.go
@@ -0,0 +1,92 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"time"
+)
+
+// DirectoryLink is an account kept by an outside directory: which one, the
+// account's id there, and whether the directory's sync is what suspended it.
+type DirectoryLink struct {
+	UserID     string
+	Directory  string // "ldap"
+	ExternalID string // an AD objectGUID
+	// SuspendedBySync is an account suspended because the directory
+	// disabled or lost it, and so reinstated when the directory has it
+	// enabled again. One an administrator suspended is not.
+	SuspendedBySync bool
+	SyncedAt        time.Time
+}
+
+// DirectoryUser is the account a directory knows by that id.
+func (s *DB) DirectoryUser(ctx context.Context, directory, externalID string) (DirectoryLink, error) {
+	var l DirectoryLink
+	var suspended int
+	var synced int64
+	err := s.db.QueryRowContext(ctx,
+		`SELECT user_id, directory, external_id, suspended_by_sync, synced_at FROM user_directory
+		 WHERE directory = ? AND external_id = ?`, directory, externalID).
+		Scan(&l.UserID, &l.Directory, &l.ExternalID, &suspended, &synced)
+	if errors.Is(err, sql.ErrNoRows) {
+		return DirectoryLink{}, ErrNotFound
+	}
+	if err != nil {
+		return DirectoryLink{}, err
+	}
+	l.SuspendedBySync, l.SyncedAt = suspended != 0, directoryTime(synced)
+	return l, nil
+}
+
+// LinkDirectory records that a directory keeps an account, by its id there.
+func (s *DB) LinkDirectory(ctx context.Context, userID, directory, externalID string, at time.Time) error {
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO user_directory (user_id, directory, external_id, synced_at) VALUES (?, ?, ?, ?)
+		 ON CONFLICT (user_id) DO UPDATE SET directory = excluded.directory, external_id = excluded.external_id,
+		   synced_at = excluded.synced_at`,
+		userID, directory, externalID, at.UnixMilli())
+	return err
+}
+
+// DirectoryLinks are every account a directory keeps.
+func (s *DB) DirectoryLinks(ctx context.Context, directory string) ([]DirectoryLink, error) {
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT user_id, directory, external_id, suspended_by_sync, synced_at FROM user_directory WHERE directory = ?`,
+		directory)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = rows.Close() }()
+	var out []DirectoryLink
+	for rows.Next() {
+		var l DirectoryLink
+		var suspended int
+		var synced int64
+		if err := rows.Scan(&l.UserID, &l.Directory, &l.ExternalID, &suspended, &synced); err != nil {
+			return nil, err
+		}
+		l.SuspendedBySync, l.SyncedAt = suspended != 0, directoryTime(synced)
+		out = append(out, l)
+	}
+	return out, rows.Err()
+}
+
+// SetSyncSuspended says whether the directory's sync is what has an account
+// suspended, and when it last looked.
+func (s *DB) SetSyncSuspended(ctx context.Context, userID string, suspended bool, at time.Time) error {
+	v := 0
+	if suspended {
+		v = 1
+	}
+	_, err := s.db.ExecContext(ctx,
+		`UPDATE user_directory SET suspended_by_sync = ?, synced_at = ? WHERE user_id = ?`, v, at.UnixMilli(), userID)
+	return err
+}
+
+func directoryTime(ms int64) time.Time {
+	if ms == 0 {
+		return time.Time{}
+	}
+	return time.UnixMilli(ms)
+}
diff --git a/internal/store/migrations/postgres/0048_user_directory.sql b/internal/store/migrations/postgres/0048_user_directory.sql
new file mode 100644
index 0000000..845c85c
--- /dev/null
+++ b/internal/store/migrations/postgres/0048_user_directory.sql
@@ -0,0 +1,14 @@
+-- Ported from the SQLite migration of the same number.
+-- Which directory keeps an account, and its id there: an Active Directory
+-- objectGUID, so a person whose mail changes there is still the same account
+-- here. suspended_by_sync is an account the directory sync suspended,
+-- because it was disabled or gone there; one an administrator suspended
+-- here is not, and is never reinstated by the sync.
+CREATE TABLE user_directory (
+  user_id           TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+  directory         TEXT NOT NULL,
+  external_id       TEXT NOT NULL,
+  suspended_by_sync INTEGER NOT NULL DEFAULT 0,
+  synced_at         BIGINT NOT NULL DEFAULT 0,
+  UNIQUE (directory, external_id)
+);
diff --git a/internal/store/migrations/sqlite/0048_user_directory.sql b/internal/store/migrations/sqlite/0048_user_directory.sql
new file mode 100644
index 0000000..ce2c3fa
--- /dev/null
+++ b/internal/store/migrations/sqlite/0048_user_directory.sql
@@ -0,0 +1,13 @@
+-- Which directory keeps an account, and its id there: an Active Directory
+-- objectGUID, so a person whose mail changes there is still the same account
+-- here. suspended_by_sync is an account the directory sync suspended,
+-- because it was disabled or gone there; one an administrator suspended
+-- here is not, and is never reinstated by the sync.
+CREATE TABLE user_directory (
+  user_id           TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+  directory         TEXT NOT NULL,
+  external_id       TEXT NOT NULL,
+  suspended_by_sync INTEGER NOT NULL DEFAULT 0,
+  synced_at         INTEGER NOT NULL DEFAULT 0,
+  UNIQUE (directory, external_id)
+);
diff --git a/internal/store/users.go b/internal/store/users.go
index ca5b90f..d34ac25 100644
--- a/internal/store/users.go
+++ b/internal/store/users.go
@@ -179,10 +179,17 @@ func (s *DB) ApproveUser(ctx context.Context, id, projectID, by string, at time.
 // signup suspended while pending and then reinstated would become active
 // without anybody approving it.
 func (s *DB) SetUserState(ctx context.Context, id string, state UserState) error {
+	// An account nobody approved is approved, not set active: that is what
+	// records who let it in. One an identity provider, SCIM or a directory
+	// made — active from the start, its password kept there ("!oidc",
+	// "!scim", "!ldap"), with no approval to record — is set active again
+	// when its provider reinstates it; refusing that left such accounts
+	// suspended for good.
 	if state == UserActive {
 		var approved sql.NullInt64
-		if err := s.db.QueryRowContext(ctx, `SELECT approved_at FROM users WHERE id = ?`, id).
-			Scan(&approved); err == nil && !approved.Valid {
+		var hash string
+		if err := s.db.QueryRowContext(ctx, `SELECT approved_at, password_hash FROM users WHERE id = ?`, id).
+			Scan(&approved, &hash); err == nil && !approved.Valid && !strings.HasPrefix(hash, "!") {
 			return errors.New("this account was never approved; approve it instead")
 		}
 	}
diff --git a/internal/web/account.go b/internal/web/account.go
index dccc110..3f09caf 100644
--- a/internal/web/account.go
+++ b/internal/web/account.go
@@ -86,6 +86,9 @@ type AccountPages struct {
 	hasQuotas bool
 	// oidc is sign-in through an identity provider; nil when there is none.
 	oidc *oidcLogin
+	// directory is the label of the directory that checks passwords
+	// (auth.ldap); empty when there is none.
+	directory string
 	// audit records every change made through these pages; nil records none.
 	audit audit.Sink
 	// hasGuard is set when /admin/guard is registered, and guardLibrary
@@ -250,6 +253,10 @@ func (p *AccountPages) signup(w http.ResponseWriter, r *http.Request) {
 // --- sign in and out ---
 
 // ssoLabel is what the sign-in button names, or "" without one.
+// SetDirectory says passwords are also checked by a directory, under this
+// label, so the sign-in form takes a username as well as a mail.
+func (p *AccountPages) SetDirectory(label string) { p.directory = label }
+
 func (p *AccountPages) ssoLabel(l *Lang) string {
 	if p.oidc == nil {
 		return ""
@@ -265,13 +272,22 @@ type loginData struct {
 	Version string
 	// SSO is the identity provider's label, when sign-in through one is on.
 	SSO string
+	// Directory is the directory's label when passwords are checked by one
+	// (auth.ldap): the field then takes a username too, not only a mail.
+	Directory string
 	// CSRF is the form's token, matched by a cookie.
 	CSRF string
 }
 
+// loginPage is what every rendering of the sign-in form carries.
+func (p *AccountPages) loginPage(w http.ResponseWriter, r *http.Request, l *Lang, email string) loginData {
+	return loginData{SSO: p.ssoLabel(l), Directory: p.directory, Email: email, SignupOpen: p.accounts.SignupOpen(),
+		Forgot: p.resets != nil, Version: p.version, CSRF: setLoginToken(w, r)}
+}
+
 func (p *AccountPages) loginForm(w http.ResponseWriter, r *http.Request) {
 	noStore(w)
-	render(w, r, "login", loginData{SSO: p.ssoLabel(langOf(r)), SignupOpen: p.accounts.SignupOpen(), Forgot: p.resets != nil, Version: p.version, CSRF: setLoginToken(w, r)})
+	render(w, r, "login", p.loginPage(w, r, langOf(r), ""))
 }
 
 func (p *AccountPages) login(w http.ResponseWriter, r *http.Request) {
@@ -281,15 +297,16 @@ func (p *AccountPages) login(w http.ResponseWriter, r *http.Request) {
 	if !loginTokenOK(r) {
 		// Not this site's form: another one posting a visitor into an
 		// account of its choosing, or a form left open past its hour.
-		renderStatus(w, r, http.StatusBadRequest, "login", loginData{SSO: p.ssoLabel(l), Email: email, SignupOpen: p.accounts.SignupOpen(), Version: p.version,
-			Error: l.T("login.err.form_expired"), CSRF: setLoginToken(w, r)})
+		d := p.loginPage(w, r, l, email)
+		d.Error = l.T("login.err.form_expired")
+		renderStatus(w, r, http.StatusBadRequest, "login", d)
 		return
 	}
 
 	ctx := account.WithClient(r.Context(), clientAddr(r))
 	token, csrf, err := p.accounts.SignIn(ctx, email, r.FormValue("password"))
 	if err != nil {
-		d := loginData{SSO: p.ssoLabel(l), Email: email, SignupOpen: p.accounts.SignupOpen(), Forgot: p.resets != nil, Version: p.version, CSRF: setLoginToken(w, r)}
+		d := p.loginPage(w, r, l, email)
 		switch {
 		case errors.Is(err, account.ErrBadCredentials),
 			errors.Is(err, account.ErrNotApproved),
@@ -309,9 +326,9 @@ func (p *AccountPages) login(w http.ResponseWriter, r *http.Request) {
 	if p.oidc != nil && p.oidc.cfg.NoPasswords {
 		if _, u, err := p.accounts.Resolve(ctx, token); err != nil || !u.IsAdmin {
 			_ = p.accounts.SignOut(ctx, token)
-			renderStatus(w, r, http.StatusForbidden, "login", loginData{SSO: p.ssoLabel(l), Email: email,
-				SignupOpen: p.accounts.SignupOpen(), Version: p.version, CSRF: setLoginToken(w, r),
-				Error: l.T("login.err.passwords_off", p.ssoLabel(l))})
+			d := p.loginPage(w, r, l, email)
+			d.Error = l.T("login.err.passwords_off", p.ssoLabel(l))
+			renderStatus(w, r, http.StatusForbidden, "login", d)
 			return
 		}
 	}
diff --git a/internal/web/locales/en/account.json b/internal/web/locales/en/account.json
index 32873e2..6aa4942 100644
--- a/internal/web/locales/en/account.json
+++ b/internal/web/locales/en/account.json
@@ -19,6 +19,8 @@
   "login.title": "Sign in · llmgw",
   "login.heading": "Sign in",
   "login.email": "Email",
+  "login.username": "Username or email",
+  "login.with_directory": "Sign in with your %s account.",
   "login.password": "Password",
   "login.submit": "Sign in",
   "login.with_sso": "Sign in with %s",
diff --git a/internal/web/locales/tr/account.json b/internal/web/locales/tr/account.json
index b56eccc..d0b6755 100644
--- a/internal/web/locales/tr/account.json
+++ b/internal/web/locales/tr/account.json
@@ -19,6 +19,8 @@
   "login.title": "Giriş yap · llmgw",
   "login.heading": "Giriş yapın",
   "login.email": "E-posta",
+  "login.username": "Kullanıcı adı veya e-posta",
+  "login.with_directory": "%s hesabınızla giriş yapın.",
   "login.password": "Parola",
   "login.submit": "Giriş yap",
   "login.with_sso": "%s ile giriş yap",
diff --git a/internal/web/oidc.go b/internal/web/oidc.go
index 63b59ef..f192a47 100644
--- a/internal/web/oidc.go
+++ b/internal/web/oidc.go
@@ -148,8 +148,9 @@ func (p *AccountPages) oidcStart(w http.ResponseWriter, r *http.Request) {
 	pr, err := o.providerFor(r.Context())
 	if err != nil {
 		p.log.Warn("the identity provider did not answer", "issuer", o.cfg.Issuer, "err", err)
-		renderStatus(w, r, http.StatusBadGateway, "login", loginData{SignupOpen: p.accounts.SignupOpen(), Version: p.version,
-			CSRF: setLoginToken(w, r), SSO: o.cfg.Label, Error: langOf(r).T("sso.err.no_answer")})
+		d := p.loginPage(w, r, langOf(r), "")
+		d.Error = langOf(r).T("sso.err.no_answer")
+		renderStatus(w, r, http.StatusBadGateway, "login", d)
 		return
 	}
 	state, nonce, verifier := randomToken(), randomToken(), oauth2.GenerateVerifier()
@@ -172,8 +173,9 @@ func (p *AccountPages) oidcCallback(w http.ResponseWriter, r *http.Request) {
 		if errors.As(err, &ae) {
 			msg = ae.in(l)
 		}
-		renderStatus(w, r, http.StatusForbidden, "login", loginData{SignupOpen: p.accounts.SignupOpen(),
-			Version: p.version, CSRF: setLoginToken(w, r), SSO: o.cfg.Label, Error: msg})
+		d := p.loginPage(w, r, l, "")
+		d.Error = msg
+		renderStatus(w, r, http.StatusForbidden, "login", d)
 	}
 	c, err := r.Cookie(oidcCookie)
 	if err != nil {
@@ -297,7 +299,17 @@ func (p *AccountPages) oidcUser(ctx context.Context, claims map[string]any) (sto
 		return store.User{}, accountError{"sso.err.state", []any{email, string(u.State)}}
 	}
 
-	groups := claimStrings(claims[or(o.cfg.GroupsClaim, "groups")])
+	claim := or(o.cfg.GroupsClaim, "groups")
+	if groupsOverflowed(claims, claim) {
+		// Read as no groups, this would take an administrator's role away
+		// at their next sign-in: kept as they are instead, and said.
+		p.log.Error("the identity provider left this person's groups out of the token, as Entra ID does past 200 groups; "+
+			"their role and memberships are left as they were. In the app registration's token configuration, "+
+			"emit only the groups assigned to the application, or provision through SCIM",
+			"email", email, "claim", claim)
+		return u, nil
+	}
+	groups := claimStrings(claims[claim])
 	if len(o.cfg.Roles) > 0 {
 		role := ""
 		for _, r := range []string{store.RoleAdmin, store.RoleOperator, store.RoleBilling, store.RoleViewer} {
@@ -333,6 +345,22 @@ func (p *AccountPages) oidcUser(ctx context.Context, claims map[string]any) (sto
 	return u, nil
 }
 
+// groupsOverflowed is a token whose groups claim was too long to send:
+// Entra ID then names a source to fetch it from (_claim_names), or, in a
+// token from the implicit flow, says only hasgroups.
+func groupsOverflowed(claims map[string]any, claim string) bool {
+	if _, ok := claims[claim]; ok {
+		return false
+	}
+	if names, ok := claims["_claim_names"].(map[string]any); ok {
+		if _, ok := names[claim]; ok {
+			return true
+		}
+	}
+	has, _ := claims["hasgroups"].(bool)
+	return has
+}
+
 // oidcPlace finds org:NAME, team:ORG/TEAM, project:ORG/TEAM/PROJECT.
 func (p *AccountPages) oidcPlace(ctx context.Context, where string) (store.Scope, string, error) {
 	kind, path, _ := strings.Cut(where, ":")
diff --git a/internal/web/oidc_test.go b/internal/web/oidc_test.go
index 6f8b736..e3b03f7 100644
--- a/internal/web/oidc_test.go
+++ b/internal/web/oidc_test.go
@@ -165,6 +165,15 @@ func TestSigningInThroughAProvider(t *testing.T) {
 		t.Error("no session cookie")
 	}
 
+	// Past 200 groups Entra ID sends none, only where to fetch them: the
+	// role stays rather than being taken away as if she had no groups.
+	idp.claims = map[string]any{"email": "ann@example.com", "email_verified": true,
+		"_claim_names":   map[string]any{"groups": "src1"},
+		"_claim_sources": map[string]any{"src1": map[string]any{"endpoint": "https://graph.windows.net/t/users/u/getMemberObjects"}}}
+	if rec := signIn(t, mux, idp, false); rec.Code != http.StatusSeeOther || st.roles[u.ID] != "operator" {
+		t.Errorf("an overflowed groups claim: %d, role %q", rec.Code, st.roles[u.ID])
+	}
+
 	// Refused: a state that is not this browser's, an unverified address,
 	// and nobody the gateway knows when it does not make accounts.
 	if rec := signIn(t, mux, idp, true); rec.Code != http.StatusForbidden {
diff --git a/internal/web/templates/account.html b/internal/web/templates/account.html
index f8b6a41..7b9441d 100644
--- a/internal/web/templates/account.html
+++ b/internal/web/templates/account.html
@@ -38,7 +38,9 @@
 {{if .Error}}<p class="error">{{.Error}}</p>{{end}}
 <form method="post" autocomplete="on">
   <input type="hidden" name="csrf" value="{{.CSRF}}">
-  <label>{{t "login.email"}}<input type="email" name="email" value="{{.Email}}" required autocomplete="email"></label>
+  {{if .Directory}}<p class="sub">{{t "login.with_directory" .Directory}}</p>
+  <label>{{t "login.username"}}<input type="text" name="email" value="{{.Email}}" required autocomplete="username" autocapitalize="none" spellcheck="false"></label>
+  {{else}}<label>{{t "login.email"}}<input type="email" name="email" value="{{.Email}}" required autocomplete="email"></label>{{end}}
   <label>{{t "login.password"}}<input type="password" name="password" required autocomplete="current-password"></label>
   <button type="submit">{{t "login.submit"}}</button>
 </form>