LDAP auth method

The ldap auth method allows authentication using an existing LDAP server and user/password credentials. This allows Vault to be integrated into environments using LDAP without duplicating the user/pass configuration in multiple places.

The mapping of groups and users in LDAP to Vault policies is managed by using the users/ and groups/ paths.

A note on escaping

It is up to the administrator to provide properly escaped DNs. This includes the user DN, bind DN for search, and so on.

The only DN escaping performed by this method is on usernames given at login time when they are inserted into the final bind DN, and uses escaping rules defined in RFC 4514.

Additionally, Active Directory has escaping rules that differ slightly from the RFC; in particular it requires escaping of '#' regardless of position in the DN (the RFC only requires it to be escaped when it is the first character), and '=', which the RFC indicates can be escaped with a backslash, but does not contain in its set of required escapes. If you are using Active Directory and these appear in your usernames, please ensure that they are escaped, in addition to being properly escaped in your configured DNs.

For reference, see RFC 4514 and this TechNet post on characters to escape in Active Directory.

Authentication

Via the CLI

$ vault login -method=ldap username=mitchellh
Password (will be hidden):
Successfully authenticated! The policies that are associated
with this token are listed below:

admins

Via the API

$ curl \
    --request POST \
    --data '{"password": "foo"}' \
    http://127.0.0.1:8200/v1/auth/ldap/login/mitchellh

The response will be in JSON. For example:

{
  "lease_id": "",
  "renewable": false,
  "lease_duration": 0,
  "data": null,
  "auth": {
    "client_token": "c4f280f6-fdb2-18eb-89d3-589e2e834cdb",
    "policies": [
      "admins"
    ],
    "metadata": {
      "username": "mitchellh"
    },
    "lease_duration": 0,
    "renewable": false
  }
}

Configuration

Auth methods must be configured in advance before users or machines can authenticate. These steps are usually completed by an operator or configuration management tool.

1. Enable the ldap auth method:

   $ vault auth enable ldap
   

2. Configure connection details for your LDAP server, information on how to authenticate users, and instructions on how to query for group membership. The configuration options are categorized and detailed below.

Connection parameters

• url (string, required) - The LDAP server to connect to. Examples: ldap://ldap.myorg.com, ldaps://ldap.myorg.com:636. This can also be a comma-delineated list of URLs, e.g. ldap://ldap.myorg.com,ldaps://ldap.myorg.com:636, in which case the servers will be tried in-order if there are errors during the connection process.
• starttls (bool, optional) - If true, issues a StartTLS command after establishing an unencrypted connection.
• insecure_tls - (bool, optional) - If true, skips LDAP server SSL certificate verification - insecure, use with caution!
• certificate - (string, optional) - CA certificate to use when verifying LDAP server certificate, must be x509 PEM encoded.
• client_tls_cert - (string, optional) - Client certificate to provide to the LDAP server, must be x509 PEM encoded.
• client_tls_key - (string, optional) - Client certificate key to provide to the LDAP server, must be x509 PEM encoded.

Binding parameters

There are two alternate methods of resolving the user object used to authenticate the end user: Search or User Principal Name. When using Search, the bind can be either anonymous or authenticated. User Principal Name is a method of specifying users supported by Active Directory. More information on UPN can be found here.

userfilter works with both authenticated and anonymous Search. In order for userfilter to apply for authenticated searches, binddn and bindpass must be set. For anonymous search, discoverdn must be set to true, and deny_null_bind must be set to false.

Binding - authenticated search

• binddn (string, optional) - Distinguished name of object to bind when performing user and group search. Example: cn=vault,ou=Users,dc=example,dc=com
• bindpass (string, optional) - Password to use along with binddn when performing user search.
• userdn (string, optional) - Base DN under which to perform user search. Example: ou=Users,dc=example,dc=com
• userattr (string, optional) - Attribute on user attribute object matching the username passed when authenticating. Examples: sAMAccountName, cn, uid
• userfilter (string, optional) - Go template used to construct a ldap user search filter. The template can access the following context variables: [UserAttr, Username]. The default userfilter is ({{.UserAttr}}={{.Username}}) or (userPrincipalName={{.Username}}@UPNDomain) if the upndomain parameter is set. The user search filter can be used to restrict what user can attempt to log in. For example, to limit login to users that are not contractors, you could write (&(objectClass=user)({{.UserAttr}}={{.Username}})(!(employeeType=Contractor))).

Binding - anonymous search

• discoverdn (bool, optional) - If true, use anonymous bind to discover the bind DN of a user
• userdn (string, optional) - Base DN under which to perform user search. Example: ou=Users,dc=example,dc=com
• userattr (string, optional) - Attribute on user attribute object matching the username passed when authenticating. Examples: sAMAccountName, cn, uid
• userfilter (string, optional) - Go template used to construct a ldap user search filter. The template can access the following context variables: [UserAttr, Username]. The default userfilter is ({{.UserAttr}}={{.Username}}) or (userPrincipalName={{.Username}}@UPNDomain) if the upndomain parameter is set. The user search filter can be used to restrict what user can attempt to log in. For example, to limit login to users that are not contractors, you could write (&(objectClass=user)({{.UserAttr}}={{.Username}})(!(employeeType=Contractor))).
• deny_null_bind (bool, optional) - This option prevents users from bypassing authentication when providing an empty password. The default is true.
• anonymous_group_search (bool, optional) - Use anonymous binds when performing LDAP group searches. Defaults to false.

Alias dereferencing

• dereference_aliases (string, optional) - Control how aliases are dereferenced when performing the search. Possible values are: never, finding, searching, and always. finding will only dereference aliases during name resolution of the base. searching will dereference aliases after name resolution.

Binding - user principal name (AD)

• upndomain (string, optional) - userPrincipalDomain used to construct the UPN string for the authenticating user. The constructed UPN will appear as [username]@UPNDomain. Example: example.com, which will cause vault to bind as username@example.com.

Group membership resolution

Once a user has been authenticated, the LDAP auth method must know how to resolve which groups the user is a member of. The configuration for this can vary depending on your LDAP server and your directory schema. There are two main strategies when resolving group membership - the first is searching for the authenticated user object and following an attribute to groups it is a member of. The second is to search for group objects of which the authenticated user is a member of. Both methods are supported.

• groupfilter (string, optional) - Go template used when constructing the group membership query. The template can access the following context variables: [UserDN, Username]. The default is (|(memberUid={{.Username}})(member={{.UserDN}})(uniqueMember={{.UserDN}})), which is compatible with several common directory schemas. To support nested group resolution for Active Directory, instead use the following query: (&(objectClass=group)(member:1.2.840.113556.1.4.1941:={{.UserDN}})).
• groupdn (string, required) - LDAP search base to use for group membership search. This can be the root containing either groups or users. Example: ou=Groups,dc=example,dc=com
• groupattr (string, optional) - LDAP attribute to follow on objects returned by groupfilter in order to enumerate user group membership. Examples: for groupfilter queries returning group objects, use: cn. For queries returning user objects, use: memberOf. The default is cn.

Note: When using Authenticated Search for binding parameters (see above) the distinguished name defined for binddn is used for the group search. Otherwise, the authenticating user is used to perform the group search.

Use vault path-help for more details.

Other

• username_as_alias (bool, optional) - If set to true, forces the auth method to use the username passed by the user as the alias name.
• max_page_size (int, optional) - If set to a value greater than 0, the LDAP backend will use the LDAP server's paged search control to request pages of up to the given size. This can be used to avoid hitting the LDAP server's maximum result size limit. Otherwise, the LDAP backend will not use the paged search control.

Examples:

Scenario 1

• LDAP server running on ldap.example.com, port 389.
• Server supports STARTTLS command to initiate encryption on the standard port.
• CA Certificate stored in file named ldap_ca_cert.pem
• Server is Active Directory supporting the userPrincipalName attribute. Users are identified as username@example.com.
• Groups are nested, we will use LDAP_MATCHING_RULE_IN_CHAIN to walk the ancestry graph.
• Group search will start under ou=Groups,dc=example,dc=com. For all group objects under that path, the member attribute will be checked for a match against the authenticated user.
• Group names are identified using their cn attribute.

$ vault write auth/ldap/config \
    url="ldap://ldap.example.com" \
    userdn="ou=Users,dc=example,dc=com" \
    groupdn="ou=Groups,dc=example,dc=com" \
    groupfilter="(&(objectClass=group)(member:1.2.840.113556.1.4.1941:={{.UserDN}}))" \
    groupattr="cn" \
    upndomain="example.com" \
    certificate=@ldap_ca_cert.pem \
    insecure_tls=false \
    starttls=true
...

Scenario 2

• LDAP server running on ldap.example.com, port 389.
• Server supports STARTTLS command to initiate encryption on the standard port.
• CA Certificate stored in file named ldap_ca_cert.pem
• Server does not allow anonymous binds for performing user search.
• Bind account used for searching is cn=vault,ou=users,dc=example,dc=com with password My$ecrt3tP4ss.
• User objects are under the ou=Users,dc=example,dc=com organizational unit.
• Username passed to vault when authenticating maps to the sAMAccountName attribute.
• Group membership will be resolved via the memberOf attribute of user objects. That search will begin under ou=Users,dc=example,dc=com.

$ vault write auth/ldap/config \
    url="ldap://ldap.example.com" \
    userattr=sAMAccountName \
    userdn="ou=Users,dc=example,dc=com" \
    groupdn="ou=Users,dc=example,dc=com" \
    groupfilter="(&(objectClass=person)(uid={{.Username}}))" \
    groupattr="memberOf" \
    binddn="cn=vault,ou=users,dc=example,dc=com" \
    bindpass='My$ecrt3tP4ss' \
    certificate=@ldap_ca_cert.pem \
    insecure_tls=false \
    starttls=true
...

Scenario 3

• LDAP server running on ldap.example.com, port 636 (LDAPS)
• CA Certificate stored in file named ldap_ca_cert.pem
• User objects are under the ou=Users,dc=example,dc=com organizational unit.
• Username passed to vault when authenticating maps to the uid attribute.
• User bind DN will be auto-discovered using anonymous binding.
• Group membership will be resolved via any one of memberUid, member, or uniqueMember attributes. That search will begin under ou=Groups,dc=example,dc=com.
• Group names are identified using the cn attribute.

$ vault write auth/ldap/config \
    url="ldaps://ldap.example.com" \
    userattr="uid" \
    userdn="ou=Users,dc=example,dc=com" \
    discoverdn=true \
    groupdn="ou=Groups,dc=example,dc=com" \
    certificate=@ldap_ca_cert.pem \
    insecure_tls=false \
    starttls=true
...

LDAP group -> policy mapping

Next we want to create a mapping from an LDAP group to a Vault policy:

$ vault write auth/ldap/groups/scientists policies=foo,bar

This maps the LDAP group "scientists" to the "foo" and "bar" Vault policies. We can also add specific LDAP users to additional (potentially non-LDAP) groups. Note that policies can also be specified on LDAP users as well.

$ vault write auth/ldap/groups/engineers policies=foobar
$ vault write auth/ldap/users/tesla groups=engineers policies=zoobar

This adds the LDAP user "tesla" to the "engineers" group, which maps to the "foobar" Vault policy. User "tesla" itself is associated with "zoobar" policy.

Finally, we can test this by authenticating:

$ vault login -method=ldap username=tesla
Password (will be hidden):
Successfully authenticated! The policies that are associated
with this token are listed below:

default, foobar, zoobar

Note on policy mapping

It should be noted that user -> policy mapping happens at token creation time. And changes in group membership on the LDAP server will not affect tokens that have already been provisioned. To see these changes, old tokens should be revoked and the user should be asked to reauthenticate.

API

The LDAP auth method has a full HTTP API. Please see the LDAP auth method API for more details.