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LDAP A reference guide on the LDAP implementation specifics This section contains reference documentation for Authelia's LDAP implementation specifics. 2022-06-17T21:03:47+10:00 false
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Binding

When it comes to LDAP there are several considerations for deciding how to bind to the LDAP server.

Unauthenticated Binding

The most insecure method is unauthenticated binds. They are generally considered insecure due to the fact allowing them at all ensures anyone with any level of network access can easily obtain objects and their attributes.

Authelia does support unauthenticated binds but it is not by default, you must configure the permit_unauthenticated_bind configuration option.

End-User Binding

One method to bind to the server that is favored by a lot of people is binding to the LDAP server as the end user. While this is more secure than methods such as Unauthenticated Binding the drawback is that it can only be used securely at the time the user enters their credentials. Storing a password in memory in general is not very secure and prone to breakage due to outside influences (i.e. the user changes their password).

In addition, this method is not compatible with the password reset / forgot password flow at all (not to be confused with a change password flow).

Authelia doesn't currently support such a binding method excluding for checking user passwords.

Service-User Binding

This is the most common method of binding to LDAP. This involves setting up a special service user with a complex password which has the minimum permissions required to do the tasks required.

Authelia primarily supports this method.

Implementation Guide

The following implementations exist:

  • custom:
    • Not specific to any particular LDAP provider
  • activedirectory:
    • Specific configuration defaults for Active Directory
    • Special implementation details:
      • Includes a special encoding format required for changing passwords with Active Directory
  • rfc2307bis:
    • Specific configuration defaults for RFC2307bis
    • No special implementation details
  • freeipa:
    • Specific configuration defaults for FreeIPA
    • No special implementation details
  • lldap:
    • Specific configuration defaults for lldap
    • No special implementation details
  • glauth:
    • Specific configuration defaults for GLAuth
    • No special implementation details

Group Search Modes

There are currently two group search modes that exist.

Search Mode: filter

The filter search mode is the default search mode. Generally this is recommended.

Search Mode: memberof

The memberof search mode is a special search mode. Generally this is discouraged and is currently experimental.

Some systems provide a memberOf attribute which may include additional groups that the user is a member of. This search mode allows using this attribute as a method to determine their groups. How it works is the search is performed against the base with the subtree scope and the groups filter must include one of the {memberof:*} replacements, and the distinguished names of the results from the search are compared (case-insensitive) against the users memberOf attribute to determine if they are members.

This means:

  1. The groups still must be in the search base that you have configured.
  2. The memberOf attribute MUST include the distinguished name of the group.
  3. If the {memberof:dn} replacement is used:
    1. The distinguished name MUST be searchable by your directory server.
  4. The first relative distinguished name of the distinguished name MUST be search

Filter replacements

Various replacements occur in the user and groups filter. The replacements either occur at startup or upon an LDAP search which is indicated by the phase column.

The phases exist to optimize performance. The replacements in the startup phase are replaced once before the connection is ever established. In addition to this, during the startup phase we purposefully check the filters for which search phase replacements exist so we only have to check if the replacement is necessary once, and we don't needlessly perform every possible replacement on every search regardless of if it's needed or not.

General filter replacements

Placeholder Phase Replacement
{distinguished_name_attribute} startup The configured distinguished name attribute
{username_attribute} startup The configured username attribute
{mail_attribute} startup The configured mail attribute
{display_name_attribute} startup The configured display name attribute
{member_of_attribute} startup The configured member of attribute
{input} search The input into the username field

Users filter replacements

Placeholder Phase Replacement
{date-time:generalized} search The current UTC time formatted as a LDAP generalized time in the format of 20060102150405.0Z
{date-time:unix} search The current time formatted as a Unix epoch
{date-time:microsoft-nt} search The current time formatted as a Microsoft NT epoch which is used by some Microsoft Active Directory attributes

Groups filter replacements

Placeholder Phase Replacement
{username} search The username from the profile lookup obtained from the username attribute
{dn} search The distinguished name from the profile lookup
{memberof:dn} search See the detailed section below
{memberof:rdn} search Only allowed with the memberof search method and contains the first relative distinguished name of every memberOf entry a use has in parenthesis
memberof:dn

Requirements:

  1. Must be using the memberof search mode.
  2. Must have the distinguished name attribute configured in Authelia.
  3. Directory server must support searching by the distinguished name attribute (many directory services DO NOT have a distinguished name attribute).
memberof:rdn

Requirements:

  1. Must be using the memberof search mode.
  2. Directory server must support searching by the first relative distinguished name as an attribute.

Splits every memberOf value to obtain the first relative distinguished name and joins all of those after surrounding them in parenthesis. This makes the general suggested filter pattern for this particular replacement (|{memberof:rdn}). The format of this value is as follows:

(<RDN>)

For example if the user has the following distinguished names in their object:

  • CN=abc,OU=groups,DC=example,DC=com
  • CN=xyz,OU=groups,DC=example,DC=com

The value will be replaced with (CN=abc)(CN=xyz) which using the suggested pattern for the filter becomes (|(CN=abc)(CN=xyz)) which will then return any user that as a CN of abc or xyz.

Defaults

The below tables describes the current attribute defaults for each implementation.

Search Base defaults

The following set defaults for the additional_users_dn and additional_groups_dn values.

Implementation Users Groups
lldap OU=people OU=groups

Attribute defaults

This table describes the attribute defaults for each implementation. i.e. the username_attribute is described by the Username column.

Implementation Username Display Name Mail Group Name Distinguished Name Member Of
custom N/A displayName mail cn N/A N/A
activedirectory sAMAccountName displayName mail cn distinguishedName memberOf
rfc2307bis uid displayName mail cn N/A memberOf
freeipa uid displayName mail cn N/A memberOf
lldap uid cn mail cn N/A memberOf
glauth cn description mail cn N/A memberOf

Filter defaults

The filters are probably the most important part to get correct when setting up LDAP. You want to exclude accounts under the following conditions:

  • The account is disabled or locked:
    • The Active Directory implementation achieves this via the (!(userAccountControl:1.2.840.113556.1.4.803:=2)) filter.
    • The FreeIPA implementation achieves this via the (!(nsAccountLock=TRUE)) filter.
    • The GLAuth implementation achieves this via the (!(accountStatus=inactive)) filter.
    • The following implementations have no suitable attribute for this as far as we're aware:
  • Their password is expired:
    • The Active Directory implementation achieves this via the (!(pwdLastSet=0)) filter.
    • The FreeIPA implementation achieves this via the (krbPasswordExpiration>={date-time:generalized}) filter.
    • The RFC2307bis implementation achieves this via the (!(pwdReset=TRUE)) filter.
    • The following implementations have no suitable attribute for this as far as we're aware:
  • Their account is expired:
    • The Active Directory implementation achieves this via the (|(!(accountExpires=*))(accountExpires=0)(accountExpires>={date-time:microsoft-nt})) filter.
    • The FreeIPA implementation achieves this via the (|(!(krbPrincipalExpiration=*))(krbPrincipalExpiration>={date-time:generalized})) filter.
    • The following implementations have no suitable attribute for this as far as we're aware:
Implementation Users Filter Groups Filter
custom N/A N/A
activedirectory (&(|({username_attribute}={input})({mail_attribute}={input}))(sAMAccountType=805306368)(!(userAccountControl:1.2.840.113556.1.4.803:=2))(!(pwdLastSet=0))(|(!(accountExpires=*))(accountExpires=0)(accountExpires>={date-time:microsoft-nt}))) (&(member={dn})(|(sAMAccountType=268435456)(sAMAccountType=536870912)))
rfc2307bis (&(|({username_attribute}={input})({mail_attribute}={input}))(|(objectClass=inetOrgPerson)(objectClass=organizationalPerson))(!(pwdReset=TRUE))) (&(|(member={dn})(uniqueMember={dn}))(|(objectClass=groupOfNames)(objectClass=groupOfUniqueNames)(objectClass=groupOfMembers)))
freeipa (&(|({username_attribute}={input})({mail_attribute}={input}))(objectClass=person)(!(nsAccountLock=TRUE))(krbPasswordExpiration>={date-time:generalized})(|(!(krbPrincipalExpiration=*))(krbPrincipalExpiration>={date-time:generalized}))) (&(member={dn})(objectClass=groupOfNames))
lldap (&(|({username_attribute}={input})({mail_attribute}={input}))(objectClass=person)) (&(member={dn})(objectClass=groupOfNames))
glauth (&(|({username_attribute}={input})({mail_attribute}={input}))(objectClass=posixAccount)(!(accountStatus=inactive))) (&(uniqueMember={dn})(objectClass=posixGroup))
Microsoft Active Directory sAMAccountType
Account Type Value Description Equivalent Filter
268435456 Global/Universal Security Group Objects N/A
536870912 Domain Local Security Group Objects N/A
805306368 Normal User Accounts (&(objectCategory=person)(objectClass=user))

References: