---
type: reference
stage: Manage
group: Access
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

# General LDAP Setup

GitLab integrates with LDAP to support user authentication.

This integration works with most LDAP-compliant directory servers, including:

- Microsoft Active Directory
- Apple Open Directory
- Open LDAP
- 389 Server

GitLab Enterprise Editions (EE) include enhanced integration,
including group membership syncing as well as multiple LDAP servers support.

NOTE: **Note:**
[Microsoft Active Directory Trusts](https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc771568(v=ws.10)) are not supported.

## Overview

[LDAP](https://en.wikipedia.org/wiki/Lightweight_Directory_Access_Protocol)
stands for **Lightweight Directory Access Protocol**, which is a standard
application protocol for accessing and maintaining distributed directory
information services over an Internet Protocol (IP) network.

## Security **(CORE ONLY)**

GitLab assumes that LDAP users:

- Are not able to change their LDAP `mail`, `email`, or `userPrincipalName` attributes.
  An LDAP user who is allowed to change their email on the LDAP server can potentially
  [take over any account](#enabling-ldap-sign-in-for-existing-gitlab-users-core-only)
  on your GitLab server.
- Have unique email addresses, otherwise it is possible for LDAP users with the same
  email address to share the same GitLab account.

We recommend against using LDAP integration if your LDAP users are
allowed to change their 'mail', 'email' or 'userPrincipalName' attribute on
the LDAP server or share email addresses.

### User deletion **(CORE ONLY)**

If a user is deleted from the LDAP server, they will be blocked in GitLab as
well. Users will be immediately blocked from logging in. However, there is an
LDAP check cache time of one hour (see note) which means users that
are already logged in or are using Git over SSH will still be able to access
GitLab for up to one hour. Manually block the user in the GitLab Admin Area to
immediately block all access.

NOTE: **Note**:
GitLab Enterprise Edition Starter supports a
[configurable sync time](#adjusting-ldap-user-sync-schedule-starter-only).

## Git password authentication **(CORE ONLY)**

LDAP-enabled users can always authenticate with Git using their GitLab username
or email and LDAP password, even if password authentication for Git is disabled
in the application settings.

## Enabling LDAP sign-in for existing GitLab users **(CORE ONLY)**

When a user signs in to GitLab with LDAP for the first time, and their LDAP
email address is the primary email address of an existing GitLab user, then
the LDAP DN will be associated with the existing user. If the LDAP email
attribute is not found in GitLab's database, a new user is created.

In other words, if an existing GitLab user wants to enable LDAP sign-in for
themselves, they should check that their GitLab email address matches their
LDAP email address, and then sign into GitLab via their LDAP credentials.

## Google Secure LDAP **(CORE ONLY)**

> Introduced in GitLab 11.9.

[Google Cloud Identity](https://cloud.google.com/identity/) provides a Secure
LDAP service that can be configured with GitLab for authentication and group sync.
See [Google Secure LDAP](google_secure_ldap.md) for detailed configuration instructions.

## Configuration **(CORE ONLY)**

To enable LDAP integration you need to add your LDAP server settings in
`/etc/gitlab/gitlab.rb` or `/home/git/gitlab/config/gitlab.yml` for Omnibus
GitLab and installations from source respectively.

There is a Rake task to check LDAP configuration. After configuring LDAP
using the documentation below, see [LDAP check Rake task](../../raketasks/check.md#ldap-check)
for information on the LDAP check Rake task.

NOTE: **Note:**
The `encryption` value `simple_tls` corresponds to 'Simple TLS' in the LDAP
library. `start_tls` corresponds to StartTLS, not to be confused with regular TLS.
Normally, if you specify `simple_tls` it will be on port 636, while `start_tls` (StartTLS)
would be on port 389. `plain` also operates on port 389. Removed values: `tls` was replaced with `start_tls` and `ssl` was replaced with `simple_tls`.

NOTE: **Note:**
LDAP users must have an email address set, regardless of whether it is used to log in.

### Example Configurations **(CORE ONLY)**

**Omnibus Configuration**

```ruby
gitlab_rails['ldap_enabled'] = true
gitlab_rails['prevent_ldap_sign_in'] = false
gitlab_rails['ldap_servers'] = {
'main' => {
  'label' => 'LDAP',
  'host' =>  'ldap.mydomain.com',
  'port' => 389,
  'uid' => 'sAMAccountName',
  'encryption' => 'simple_tls',
  'verify_certificates' => true,
  'bind_dn' => '_the_full_dn_of_the_user_you_will_bind_with',
  'password' => '_the_password_of_the_bind_user',
  'encryption' => 'plain',
  'verify_certificates' => true,
  'tls_options' => {
    'ca_file' => '',
    'ssl_version' => '',
    'ciphers' => '',
    'cert' => '',
    'key' => ''
  },
  'timeout' => 10,
  'active_directory' => true,
  'allow_username_or_email_login' => false,
  'block_auto_created_users' => false,
  'base' => 'dc=example,dc=com',
  'user_filter' => '',
  'attributes' => {
    'username' => ['uid', 'userid', 'sAMAccountName'],
    'email' => ['mail', 'email', 'userPrincipalName'],
    'name' => 'cn',
    'first_name' => 'givenName',
    'last_name' => 'sn'
  },
  'lowercase_usernames' => false,

  # EE Only
  'group_base' => '',
  'admin_group' => '',
  'external_groups' => [],
  'sync_ssh_keys' => false
  }
}
```

**Source Configuration**

```yaml
production:
  # snip...
  ldap:
    enabled: false
    prevent_ldap_sign_in: false
    servers:
      main:
        label: 'LDAP'
        ...
```

### Basic Configuration Settings **(CORE ONLY)**

| Setting | Description | Required | Examples |
| ------- | ----------- | -------- | -------- |
| `label` | A human-friendly name for your LDAP server. It will be displayed on your login page. | yes | `'Paris'` or `'Acme, Ltd.'` |
| `host`  | IP address or domain name of your LDAP server. | yes | `'ldap.mydomain.com'` |
| `port`  | The port to connect with on your LDAP server. Always an integer, not a string. | yes | `389` or `636` (for SSL) |
| `uid`   | LDAP attribute for username. Should be the attribute, not the value that maps to the `uid`. | yes | `'sAMAccountName'`, `'uid'`, `'userPrincipalName'` |
| `bind_dn` | The full DN of the user you will bind with. | no | `'america\momo'` or `'CN=Gitlab,OU=Users,DC=domain,DC=com'` |
| `password` | The password of the bind user. | no | `'your_great_password'` |
| `encryption` | Encryption method. The `method` key is deprecated in favor of `encryption`. | yes | `'start_tls'` or `'simple_tls'` or `'plain'` |
| `verify_certificates` | Enables SSL certificate verification if encryption method is `start_tls` or `simple_tls`. Defaults to true. | no | boolean |
| `timeout` | Set a timeout, in seconds, for LDAP queries. This helps avoid blocking a request if the LDAP server becomes unresponsive. A value of 0 means there is no timeout. | no | `10` or `30` |
| `active_directory` | This setting specifies if LDAP server is Active Directory LDAP server. For non-AD servers it skips the AD specific queries. If your LDAP server is not AD, set this to false. | no | boolean |
| `allow_username_or_email_login` | If enabled, GitLab will ignore everything after the first `@` in the LDAP username submitted by the user on login. If you are using `uid: 'userPrincipalName'` on ActiveDirectory you need to disable this setting, because the userPrincipalName contains an `@`. | no | boolean |
| `block_auto_created_users` | To maintain tight control over the number of active users on your GitLab installation, enable this setting to keep new users blocked until they have been cleared by the admin (default: false). | no | boolean |
| `base` | Base where we can search for users. | yes | `'ou=people,dc=gitlab,dc=example'` or `'DC=mydomain,DC=com'` |
| `user_filter` | Filter LDAP users. Format: [RFC 4515](https://tools.ietf.org/search/rfc4515) Note: GitLab does not support `omniauth-ldap`'s custom filter syntax. | no | `'(employeeType=developer)'` or `'(&(objectclass=user)(|(samaccountname=momo)(samaccountname=toto)))'` |
| `lowercase_usernames` | If lowercase_usernames is enabled, GitLab will lower case the username. | no | boolean |

### SSL Configuration Settings **(CORE ONLY)**

| Setting | Description | Required | Examples |
| ------- | ----------- | -------- | -------- |
| `ca_file` | Specifies the path to a file containing a PEM-format CA certificate, e.g. if you need to use an internal CA. | no | `'/etc/ca.pem'` |
| `ssl_version` | Specifies the SSL version for OpenSSL to use, if the OpenSSL default is not appropriate. | no | `'TLSv1_1'` |
| `ciphers` | Specific SSL ciphers to use in communication with LDAP servers. | no | `'ALL:!EXPORT:!LOW:!aNULL:!eNULL:!SSLv2'` |
| `cert` | Client certificate | no | `'-----BEGIN CERTIFICATE----- <REDACTED> -----END CERTIFICATE -----'` |
| `key` | Client private key | no | `'-----BEGIN PRIVATE KEY----- <REDACTED> -----END PRIVATE KEY -----'` |

### Attribute Configuration Settings **(CORE ONLY)**

LDAP attributes that GitLab will use to create an account for the LDAP user. The specified attribute can either be the attribute name as a string (e.g. `'mail'`), or an array of attribute names to try in order (e.g. `['mail', 'email']`). Note that the user's LDAP login will always be the attribute specified as `uid` above.

| Setting | Description | Required | Examples |
| ------- | ----------- | -------- | -------- |
| `username` | The username will be used in paths for the user's own projects (like `gitlab.example.com/username/project`) and when mentioning them in issues, merge request and comments (like `@username`). If the attribute specified for `username` contains an email address, the GitLab username will be the part of the email address before the `@`. | no | `['uid', 'userid', 'sAMAccountName']` |
| `email` | LDAP attribute for user email. | no | `['mail', 'email', 'userPrincipalName']` |
| `name` | LDAP attribute for user display name. If no full name could be found at the attribute specified for `name`, the full name is determined using the attributes specified for `first_name` and `last_name`. | no | `'cn'` or `'displayName'` |
| `first_name` | LDAP attribute for user first name. | no | `'givenName'` |
| `last_name` | LDAP attribute for user last name. | no | `'sn'` |

### LDAP Sync Configuration Settings **(STARTER ONLY)**

| Setting | Description | Required | Examples |
| ------- | ----------- | -------- | -------- |
| `group_base` | Base used to search for groups. | no | `'ou=groups,dc=gitlab,dc=example'` |
| `admin_group` | The CN of a group containing GitLab administrators. Note: Not `cn=administrators` or the full DN. | no | `'administrators'` |
| `external_groups` | An array of CNs of groups containing users that should be considered external. Note: Not `cn=interns` or the full DN. | no | `['interns', 'contractors']` |
| `sync_ssh_keys` | The LDAP attribute containing a user's public SSH key. | no | `'sshPublicKey'` or false if not set |

### Set up LDAP user filter **(CORE ONLY)**

If you want to limit all GitLab access to a subset of the LDAP users on your
LDAP server, the first step should be to narrow the configured `base`. However,
it is sometimes necessary to filter users further. In this case, you can set up
an LDAP user filter. The filter must comply with
[RFC 4515](https://tools.ietf.org/search/rfc4515).

**Omnibus configuration**

```ruby
gitlab_rails['ldap_servers'] = {
'main' => {
  # snip...
  'user_filter' => '(employeeType=developer)'
  }
}
```

**Source configuration**

```yaml
production:
  ldap:
    servers:
      main:
        # snip...
        user_filter: '(employeeType=developer)'
```

If you want to limit access to the nested members of an Active Directory
group, you can use the following syntax:

```plaintext
(memberOf:1.2.840.113556.1.4.1941:=CN=My Group,DC=Example,DC=com)
```

For more information about this "LDAP_MATCHING_RULE_IN_CHAIN" filter, see the following
[Microsoft Search Filter Syntax](https://docs.microsoft.com/en-us/windows/win32/adsi/search-filter-syntax) document.
Support for nested members in the user filter should not be confused with
[group sync nested groups support](#supported-ldap-group-typesattributes). **(STARTER ONLY)**

Please note that GitLab does not support the custom filter syntax used by
OmniAuth LDAP.

#### Escaping special characters **(CORE ONLY)**

The `user_filter` DN can contain special characters. For example:

- A comma:

  ```plaintext
  OU=GitLab, Inc,DC=gitlab,DC=com
  ```

- Open and close brackets:

  ```plaintext
  OU=Gitlab (Inc),DC=gitlab,DC=com
  ```

  These characters must be escaped as documented in
  [RFC 4515](https://tools.ietf.org/search/rfc4515).

- Escape commas with `\2C`. For example:

  ```plaintext
  OU=GitLab\2C Inc,DC=gitlab,DC=com
  ```

- Escape open and close brackets with `\28` and `\29`, respectively. For example:

  ```plaintext
  OU=Gitlab \28Inc\29,DC=gitlab,DC=com
  ```

### Enabling LDAP username lowercase **(CORE ONLY)**

Some LDAP servers, depending on their configurations, can return uppercase usernames.
This can lead to several confusing issues such as creating links or namespaces with uppercase names.

GitLab can automatically lowercase usernames provided by the LDAP server by enabling
the configuration option `lowercase_usernames`. By default, this configuration option is `false`.

**Omnibus configuration**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_servers'] = {
   'main' => {
     # snip...
     'lowercase_usernames' => true
     }
   }
   ```

1. [Reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect.

**Source configuration**

1. Edit `config/gitlab.yaml`:

   ```yaml
   production:
     ldap:
       servers:
         main:
           # snip...
           lowercase_usernames: true
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

### Disable LDAP web sign in **(CORE ONLY)**

It can be useful to prevent using LDAP credentials through the web UI when
an alternative such as SAML is preferred. This allows LDAP to be used for group
sync, while also allowing your SAML identity provider to handle additional
checks like custom 2FA.

When LDAP web sign in is disabled, users will not see a **LDAP** tab on the sign in page.
This does not disable [using LDAP credentials for Git access](#git-password-authentication-core-only).

**Omnibus configuration**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['prevent_ldap_sign_in'] = true
   ```

1. [Reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect.

**Source configuration**

1. Edit `config/gitlab.yaml`:

   ```yaml
   production:
     ldap:
       prevent_ldap_sign_in: true
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

## Encryption **(CORE ONLY)**

### TLS Server Authentication

There are two encryption methods, `simple_tls` and `start_tls`.

For either encryption method, if setting `verify_certificates: false`, TLS
encryption is established with the LDAP server before any LDAP-protocol data is
exchanged but no validation of the LDAP server's SSL certificate is performed.

### Limitations

#### TLS Client Authentication

Not implemented by `Net::LDAP`.

You should disable anonymous LDAP authentication and enable simple or SASL
authentication. The TLS client authentication setting in your LDAP server cannot
be mandatory and clients cannot be authenticated with the TLS protocol.

## Multiple LDAP servers **(STARTER ONLY)**

With GitLab Enterprise Edition Starter, you can configure multiple LDAP servers
that your GitLab instance will connect to.

To add another LDAP server:

1. Duplicate the settings under [the main configuration](#configuration-core-only).
1. Edit them to match the additional LDAP server.

Be sure to choose a different provider ID made of letters a-z and numbers 0-9.
This ID will be stored in the database so that GitLab can remember which LDAP
server a user belongs to.

![Multiple LDAP Servers Login](img/multi_login.gif)

Based on the example illustrated on the image above,
our `gitlab.rb` configuration would look like:

```ruby
gitlab_rails['ldap_enabled'] = true
gitlab_rails['ldap_servers'] = {
'main' => {
  'label' => 'GitLab AD',
  'host' =>  'ad.example.org',
  'port' => 636,
  ...
  },

'secondary' => {
  'label' => 'GitLab Secondary AD',
  'host' =>  'ad-secondary.example.net',
  'port' => 636,
  ...
  },

'tertiary' => {
  'label' => 'GitLab Tertiary AD',
  'host' =>  'ad-tertiary.example.net',
  'port' => 636,
  ...
  }
  
}
```

NOTE: **Note:**
Any number of LDAP servers can be configured. However, make sure to use a unique naming convention for the `label` section of each entry as this will be the display name of the tab shown on the sign-in page.

## User sync **(STARTER ONLY)**

Once per day, GitLab runs a worker to check and update GitLab
users against LDAP.

The process executes the following access checks:

- Ensure the user is still present in LDAP.
- If the LDAP server is Active Directory, ensure the user is active (not
  blocked/disabled state). This will only be checked if
  `active_directory: true` is set in the LDAP configuration.

NOTE: **Note:**
In Active Directory, a user is marked as disabled/blocked if the user
account control attribute (`userAccountControl:1.2.840.113556.1.4.803`)
has bit 2 set. See <https://ctovswild.com/2009/09/03/bitmask-searches-in-ldap/>
for more information.

The user will be set to `ldap_blocked` state in GitLab if the above conditions
fail. This means the user will not be able to login or push/pull code.

The process will also update the following user information:

- Email address.
- If `sync_ssh_keys` is set, SSH public keys.
- If Kerberos is enabled, Kerberos identity.

NOTE: **Note:**
The LDAP sync process updates existing users while new users are created on first sign in.

### Adjusting LDAP user sync schedule **(STARTER ONLY)**

NOTE: **Note:**
These are cron formatted values. You can use a crontab generator to create
these values, for example <http://www.crontabgenerator.com/>.

By default, GitLab will run a worker once per day at 01:30 a.m. server time to
check and update GitLab users against LDAP.

You can manually configure LDAP user sync times by setting the
following configuration values. The example below shows how to set LDAP user
sync to run once every 12 hours at the top of the hour.

**Omnibus installations**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_sync_worker_cron'] = "0 */12 * * *"
   ```

1. [Reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect.

**Source installations**

1. Edit `config/gitlab.yaml`:

   ```yaml
   cron_jobs:
     ldap_sync_worker_cron:
       "0 */12 * * *"
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

## Group Sync **(STARTER ONLY)**

If your LDAP supports the `memberof` property, when the user signs in for the
first time GitLab will trigger a sync for groups the user should be a member of.
That way they don't need to wait for the hourly sync to be granted
access to their groups and projects.

A group sync process will run every hour on the hour, and `group_base` must be set
in LDAP configuration for LDAP synchronizations based on group CN to work. This allows
GitLab group membership to be automatically updated based on LDAP group members.

The `group_base` configuration should be a base LDAP 'container', such as an
'organization' or 'organizational unit', that contains LDAP groups that should
be available to GitLab. For example, `group_base` could be
`ou=groups,dc=example,dc=com`. In the config file it will look like the
following.

**Omnibus configuration**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_servers'] = {
   'main' => {
     # snip...
     'group_base' => 'ou=groups,dc=example,dc=com',
     }
   }
   ```

1. [Apply your changes to GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure).

**Source configuration**

1. Edit `/home/git/gitlab/config/gitlab.yml`:

   ```yaml
   production:
     ldap:
       servers:
         main:
           # snip...
           group_base: ou=groups,dc=example,dc=com
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

To take advantage of group sync, group owners or maintainers will need to [create one
or more LDAP group links](#adding-group-links-starter-only).

### Adding group links **(STARTER ONLY)**

For information on adding group links via CNs and filters, refer to [the GitLab groups documentation](../../../user/group/index.md#manage-group-memberships-via-ldap).

### Administrator sync **(STARTER ONLY)**

As an extension of group sync, you can automatically manage your global GitLab
administrators. Specify a group CN for `admin_group` and all members of the
LDAP group will be given administrator privileges. The configuration will look
like the following.

NOTE: **Note:**
Administrators will not be synced unless `group_base` is also
specified alongside `admin_group`. Also, only specify the CN of the admin
group, as opposed to the full DN.

**Omnibus configuration**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_servers'] = {
   'main' => {
     # snip...
     'group_base' => 'ou=groups,dc=example,dc=com',
     'admin_group' => 'my_admin_group',
     }
   }
   ```

1. [Apply your changes to GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure).

**Source configuration**

1. Edit `/home/git/gitlab/config/gitlab.yml`:

   ```yaml
   production:
     ldap:
       servers:
         main:
           # snip...
           group_base: ou=groups,dc=example,dc=com
           admin_group: my_admin_group
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

### Global group memberships lock **(STARTER ONLY)**

"Lock memberships to LDAP synchronization" setting allows instance administrators
to lock down user abilities to invite new members to a group.

When enabled, the following applies:

- Only administrator can manage memberships of any group including access levels.
- Users are not allowed to share project with other groups or invite members to
  a project created in a group.

### Adjusting LDAP group sync schedule **(STARTER ONLY)**

NOTE: **Note:**
These are cron formatted values. You can use a crontab generator to create
these values, for example [Crontab Generator](http://www.crontabgenerator.com/).

By default, GitLab runs a group sync process every hour, on the hour.

CAUTION: **Important:**
It's recommended that you do not start the sync process too frequently as this
could lead to multiple syncs running concurrently. This is primarily a concern
for installations with a large number of LDAP users. Please review the
[LDAP group sync benchmark metrics](#benchmarks) to see how
your installation compares before proceeding.

You can manually configure LDAP group sync times by setting the
following configuration values. The example below shows how to set group
sync to run once every 2 hours at the top of the hour.

**Omnibus installations**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_group_sync_worker_cron'] = "0 */2 * * * *"
   ```

1. [Reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect.

**Source installations**

1. Edit `config/gitlab.yaml`:

   ```yaml
   cron_jobs:
     ldap_group_sync_worker_cron:
         "*/30 * * * *"
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

### External groups **(STARTER ONLY)**

Using the `external_groups` setting will allow you to mark all users belonging
to these groups as [external users](../../../user/permissions.md#external-users-core-only).
Group membership is checked periodically through the `LdapGroupSync` background
task.

**Omnibus configuration**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   gitlab_rails['ldap_servers'] = {
   'main' => {
     # snip...
     'external_groups' => ['interns', 'contractors'],
     }
   }
   ```

1. [Apply your changes to GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure).

**Source configuration**

1. Edit `config/gitlab.yaml`:

   ```yaml
   production:
     ldap:
       servers:
         main:
           # snip...
           external_groups: ['interns', 'contractors']
   ```

1. [Restart GitLab](../../restart_gitlab.md#installations-from-source) for the changes to take effect.

### Group sync technical details

There is a lot going on with group sync 'under the hood'. This section
outlines what LDAP queries are executed and what behavior you can expect
from group sync.

Group member access will be downgraded from a higher level if their LDAP group
membership changes. For example, if a user has 'Owner' rights in a group and the
next group sync reveals they should only have 'Developer' privileges, their
access will be adjusted accordingly. The only exception is if the user is the
*last* owner in a group. Groups need at least one owner to fulfill
administrative duties.

#### Supported LDAP group types/attributes

GitLab supports LDAP groups that use member attributes:

- `member`
- `submember`
- `uniquemember`
- `memberof`
- `memberuid`.

This means group sync supports, at least, LDAP groups with the following object classes:
`groupOfNames`, `posixGroup`, and `groupOfUniqueNames`.

Other object classes should work fine as long as members
are defined as one of the mentioned attributes. This also means GitLab supports
Microsoft Active Directory, Apple Open Directory, Open LDAP, and 389 Server.
Other LDAP servers should work, too.

Active Directory also supports nested groups. Group sync will recursively
resolve membership if `active_directory: true` is set in the configuration file.

NOTE: **Note:**
Nested group memberships are resolved only if the nested group
is found within the configured `group_base`. For example, if GitLab sees a
nested group with DN `cn=nested_group,ou=special_groups,dc=example,dc=com` but
the configured `group_base` is `ou=groups,dc=example,dc=com`, `cn=nested_group`
is ignored.

#### Queries

- Each LDAP group is queried a maximum of one time with base `group_base` and
  filter `(cn=<cn_from_group_link>)`.
- If the LDAP group has the `memberuid` attribute, GitLab will execute another
  LDAP query per member to obtain each user's full DN. These queries are
  executed with base `base`, scope 'base object', and a filter depending on
  whether `user_filter` is set. Filter may be `(uid=<uid_from_group>)` or a
  joining of `user_filter`.

#### Benchmarks

Group sync was written to be as performant as possible. Data is cached, database
queries are optimized, and LDAP queries are minimized. The last benchmark run
revealed the following metrics:

For 20000 LDAP users, 11000 LDAP groups and 1000 GitLab groups with 10
LDAP group links each:

- Initial sync (no existing members assigned in GitLab) took 1.8 hours
- Subsequent syncs (checking membership, no writes) took 15 minutes

These metrics are meant to provide a baseline and performance may vary based on
any number of factors. This was a pretty extreme benchmark and most instances will
not have near this many users or groups. Disk speed, database performance,
network and LDAP server response time will affect these metrics.

## Troubleshooting

Please see our [administrator guide to troubleshooting LDAP](ldap-troubleshooting.md).
