Refactor LDAP docs

doc/administration/auth/ldap.md

+[//]: # (Do *NOT* modify this file in EE documentation. All changes in this)
+[//]: # (file should happen in CE, too. If the change is EE-specific, put)
+[//]: # (it in `ldap-ee.md`.)
+
 # LDAP
 
 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,
-and 389 Server. GitLab EE includes enhanced integration, including group
-membership syncing.
+and 389 Server. GitLab Enterprise Editions include enhanced integration,
+including group membership syncing as well as multiple LDAP servers support.
+
+## GitLab EE
+
+The information on this page is relevant for both GitLab CE and EE. For more
+details about EE-specific LDAP features, see the
+[LDAP Enterprise Edition documentation](https://docs.gitlab.com/ee/administration/auth/ldap-ee.html).
 
 ## Security
 
@@ -27,8 +37,10 @@ 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**: GitLab EE supports a configurable sync time, with a default
-of one hour.
+NOTE: **Note**:
+GitLab Enterprise Edition Starter supports a
+[configurable sync time](https://docs.gitlab.com/ee/administration/auth/ldap-ee.html#adjusting-ldap-user-and-group-sync-schedules),
+with a default of one hour.
 
 ## Git password authentication
 
@@ -38,19 +50,21 @@ in the application settings.
 
 ## Configuration
 
+NOTE: **Note**:
+In GitLab Enterprise Edition Starter, you can configure multiple LDAP servers
+to connect to one GitLab server.
+
 For a complete guide on configuring LDAP with GitLab Community Edition, please check
 the admin guide [How to configure LDAP with GitLab CE](how_to_configure_ldap_gitlab_ce/index.md).
 
 To enable LDAP integration you need to add your LDAP server settings in
-`/etc/gitlab/gitlab.rb` or `/home/git/gitlab/config/gitlab.yml`.
+`/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**: In GitLab EE, you can configure multiple LDAP servers to connect to
-one GitLab server.
-
 Prior to version 7.4, GitLab used a different syntax for configuring
 LDAP integration. The old LDAP integration syntax still works but may be
 removed in a future version. If your `gitlab.rb` or `gitlab.yml` file contains
@@ -61,159 +75,202 @@ The configuration inside `gitlab_rails['ldap_servers']` below is sensitive to
 incorrect indentation. Be sure to retain the indentation given in the example.
 Copy/paste can sometimes cause problems.
 
+NOTE: **Note:**
+The `encryption` value `ssl` corresponds to 'Simple TLS' in the LDAP
+library. `tls` corresponds to StartTLS, not to be confused with regular TLS.
+Normally, if you specify `ssl` it will be on port 636, while `tls` (StartTLS)
+would be on port 389. `plain` also operates on port 389.
+
 **Omnibus configuration**
 
 ```ruby
 gitlab_rails['ldap_enabled'] = true
 gitlab_rails['ldap_servers'] = YAML.load <<-EOS # remember to close this block with 'EOS' below
-main: # 'main' is the GitLab 'provider ID' of this LDAP server
-  ## label
-  #
-  # A human-friendly name for your LDAP server. It is OK to change the label later,
-  # for instance if you find out it is too large to fit on the web page.
-  #
-  # Example: 'Paris' or 'Acme, Ltd.'
+##
+## 'main' is the GitLab 'provider ID' of this LDAP server
+##
+main:
+  ##
+  ## A human-friendly name for your LDAP server. It is OK to change the label later,
+  ## for instance if you find out it is too large to fit on the web page.
+  ##
+  ## Example: 'Paris' or 'Acme, Ltd.'
+  ##
   label: 'LDAP'
 
-  # Example: 'ldap.mydomain.com'
+  ##
+  ## Example: 'ldap.mydomain.com'
+  ##
   host: '_your_ldap_server'
-  # This port is an example, it is sometimes different but it is always an integer and not a string
+
+  ##
+  ## This port is an example, it is sometimes different but it is always an
+  ## integer and not a string.
+  ##
   port: 389 # usually 636 for SSL
   uid: 'sAMAccountName' # This should be the attribute, not the value that maps to uid.
 
-  # Examples: 'america\\momo' or 'CN=Gitlab Git,CN=Users,DC=mydomain,DC=com'
+  ##
+  ## Examples: 'america\\momo' or 'CN=Gitlab Git,CN=Users,DC=mydomain,DC=com'
+  ##
   bind_dn: '_the_full_dn_of_the_user_you_will_bind_with'
   password: '_the_password_of_the_bind_user'
 
-  # Encryption method. The "method" key is deprecated in favor of
-  # "encryption".
-  #
-  #   Examples: "start_tls" or "simple_tls" or "plain"
-  #
-  #   Deprecated values: "tls" was replaced with "start_tls" and "ssl" was
-  #   replaced with "simple_tls".
-  #
+  ##
+  ## Encryption method. The "method" key is deprecated in favor of
+  ## "encryption".
+  ##
+  ##   Examples: "start_tls" or "simple_tls" or "plain"
+  ##
+  ##   Deprecated values: "tls" was replaced with "start_tls" and "ssl" was
+  ##   replaced with "simple_tls".
+  ##
+  ##
   encryption: 'plain'
 
-  # Enables SSL certificate verification if encryption method is
-  # "start_tls" or "simple_tls". Defaults to true since GitLab 10.0 for
-  # security. This may break installations upon upgrade to 10.0, that did
-  # not know their LDAP SSL certificates were not setup properly. For
-  # example, when using self-signed certificates, the ca_file path may
-  # need to be specified.
+  ##
+  ## Enables SSL certificate verification if encryption method is
+  ## "start_tls" or "simple_tls". Defaults to true since GitLab 10.0 for
+  ## security. This may break installations upon upgrade to 10.0, that did
+  ## not know their LDAP SSL certificates were not setup properly.
+  ##
   verify_certificates: true
 
-  # Specifies the path to a file containing a PEM-format CA certificate,
-  # e.g. if you need to use an internal CA.
-  #
-  #   Example: '/etc/ca.pem'
-  #
-  ca_file: ''
-
-  # Specifies the SSL version for OpenSSL to use, if the OpenSSL default
-  # is not appropriate.
-  #
-  #   Example: 'TLSv1_1'
-  #
+  ##
+  ## Specifies the SSL version for OpenSSL to use, if the OpenSSL default
+  ## is not appropriate.
+  ##
+  ##   Example: 'TLSv1_1'
+  ##
+  ##
   ssl_version: ''
 
-  # 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.
+  ##
+  ## 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.
+  ##
   timeout: 10
 
-  # 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.
+  ##
+  ## 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.
+  ##
   active_directory: true
 
-  # If allow_username_or_email_login is enabled, GitLab will ignore everything
-  # after the first '@' in the LDAP username submitted by the user on login.
-  #
-  # Example:
-  # - the user enters 'jane.doe@example.com' and 'p@ssw0rd' as LDAP credentials;
-  # - GitLab queries the LDAP server with 'jane.doe' and 'p@ssw0rd'.
-  #
-  # If you are using "uid: 'userPrincipalName'" on ActiveDirectory you need to
-  # disable this setting, because the userPrincipalName contains an '@'.
+  ##
+  ## If allow_username_or_email_login is enabled, GitLab will ignore everything
+  ## after the first '@' in the LDAP username submitted by the user on login.
+  ##
+  ## Example:
+  ## - the user enters 'jane.doe@example.com' and 'p@ssw0rd' as LDAP credentials;
+  ## - GitLab queries the LDAP server with 'jane.doe' and 'p@ssw0rd'.
+  ##
+  ## If you are using "uid: 'userPrincipalName'" on ActiveDirectory you need to
+  ## disable this setting, because the userPrincipalName contains an '@'.
+  ##
   allow_username_or_email_login: false
 
-  # 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).
+  ##
+  ## 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).
+  ##
   block_auto_created_users: false
 
-  # Base where we can search for users
-  #
-  #   Ex. 'ou=People,dc=gitlab,dc=example' or 'DC=mydomain,DC=com'
-  #
+  ##
+  ## Base where we can search for users
+  ##
+  ##   Ex. 'ou=People,dc=gitlab,dc=example' or 'DC=mydomain,DC=com'
+  ##
+  ##
   base: ''
 
-  # Filter LDAP users
-  #
-  #   Format: RFC 4515 https://tools.ietf.org/search/rfc4515
-  #   Ex. (employeeType=developer)
-  #
-  #   Note: GitLab does not support omniauth-ldap's custom filter syntax.
-  #
-  #   Example for getting only specific users:
-  #   '(&(objectclass=user)(|(samaccountname=momo)(samaccountname=toto)))'
-  #
+  ##
+  ## Filter LDAP users
+  ##
+  ##   Format: RFC 4515 https://tools.ietf.org/search/rfc4515
+  ##   Ex. (employeeType=developer)
+  ##
+  ##   Note: GitLab does not support omniauth-ldap's custom filter syntax.
+  ##
+  ##   Example for getting only specific users:
+  ##   '(&(objectclass=user)(|(samaccountname=momo)(samaccountname=toto)))'
+  ##
   user_filter: ''
 
-  # 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.
+  ##
+  ## 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.
+  ##
   attributes:
-    # 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 '@'.
+    ##
+    ## 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 '@'.
+    ##
     username: ['uid', 'userid', 'sAMAccountName']
     email:    ['mail', 'email', 'userPrincipalName']
 
-    # 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`.
+    ##
+    ## 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`.
+    ##
     name:       'cn'
     first_name: 'givenName'
     last_name:  'sn'
 
-  # If lowercase_usernames is enabled, GitLab will lower case the username.
+  ##
+  ## If lowercase_usernames is enabled, GitLab will lower case the username.
+  ##
   lowercase_usernames: false
 
-
+  ##
   ## EE only
+  ##
 
-  # Base where we can search for groups
-  #
-  #   Ex. ou=groups,dc=gitlab,dc=example
-  #
+  ## Base where we can search for groups
+  ##
+  ##   Ex. ou=groups,dc=gitlab,dc=example
+  ##
   group_base: ''
 
-  # The CN of a group containing GitLab administrators
-  #
-  #   Ex. administrators
-  #
-  #   Note: Not `cn=administrators` or the full DN
-  #
+  ## The CN of a group containing GitLab administrators
+  ##
+  ##   Ex. administrators
+  ##
+  ##   Note: Not `cn=administrators` or the full DN
+  ##
   admin_group: ''
 
-  # The LDAP attribute containing a user's public SSH key
-  #
-  #   Ex. ssh_public_key
-  #
+  ## An array of CNs of groups containing users that should be considered external
+  ##
+  ##   Ex. ['interns', 'contractors']
+  ##
+  ##   Note: Not `cn=interns` or the full DN
+  ##
+  external_groups: []
+
+  ##
+  ## The LDAP attribute containing a user's public SSH key
+  ##
+  ##   Example: sshPublicKey
+  ##
   sync_ssh_keys: false
 
-# GitLab EE only: add more LDAP servers
-# Choose an ID made of a-z and 0-9 . This ID will be stored in the database
-# so that GitLab can remember which LDAP server a user belongs to.
-# uswest2:
-#   label:
-#   host:
-#   ....
+## GitLab EE only: add more LDAP servers
+## Choose an ID made of a-z and 0-9 . This ID will be stored in the database
+## so that GitLab can remember which LDAP server a user belongs to.
+#uswest2:
+#  label:
+#  host:
+#  ....
 EOS
 ```
 
@@ -222,21 +279,23 @@ EOS
 Use the same format as `gitlab_rails['ldap_servers']` for the contents under
 `servers:` in the example below:
 
-```
+```yaml
 production:
   # snip...
   ldap:
     enabled: false
     servers:
-      main: # 'main' is the GitLab 'provider ID' of this LDAP server
-        ## label
-        #
-        # A human-friendly name for your LDAP server. It is OK to change the label later,
-        # for instance if you find out it is too large to fit on the web page.
-        #
-        # Example: 'Paris' or 'Acme, Ltd.'
+      ##
+      ## 'main' is the GitLab 'provider ID' of this LDAP server
+      ##
+      main:
+        ##
+        ## A human-friendly name for your LDAP server. It is OK to change the label later,
+        ## for instance if you find out it is too large to fit on the web page.
+        ##
+        ## Example: 'Paris' or 'Acme, Ltd.'
         label: 'LDAP'
-        # snip...
+        ## snip...
 ```
 
 ## Using an LDAP filter to limit access to your GitLab server
@@ -283,6 +342,24 @@ nested members in the user filter should not be confused with
 Please note that GitLab does not support the custom filter syntax used by
 omniauth-ldap.
 
+### Escaping special characters
+
+If the `user_filter` DN contains special characters. For example, a comma:
+
+```
+OU=GitLab, Inc,DC=gitlab,DC=com
+```
+
+This character needs to be escaped as documented in [RFC 4515](https://tools.ietf.org/search/rfc4515).
+
+Due to the way the string is parsed, the special character needs to be converted
+to hex and `\\5C\\` (`5C` = `\` in hex) added before it.
+As an example the above DN would look like
+
+```
+OU=GitLab\\5C\\2C Inc,DC=gitlab,DC=com
+```
+
 ## Enabling LDAP sign-in for existing GitLab users
 
 When a user signs in to GitLab with LDAP for the first time, and their LDAP