` where scheme is either `ldap` or `ldaps`.
If utilising an IPv6 literal address it must be enclosed by square brackets:
```yaml
url: ldap://[fd00:1111:2222:3333::1]
```
### start_tls
type: boolean
{: .label .label-config .label-purple }
default: false
{: .label .label-config .label-blue }
required: no
{: .label .label-config .label-green }
Enables use of the LDAP StartTLS process which is not commonly used. You should only configure this if you know you need
it. The initial connection will be over plain text, and Authelia will try to upgrade it with the LDAP server. LDAPS
URL's are slightly more secure.
### tls
Controls the TLS connection validation process. You can see how to configure the tls
section [here](../index.md#tls-configuration).
### base_dn
type: string
{: .label .label-config .label-purple }
required: yes
{: .label .label-config .label-red }
Sets the base distinguished name container for all LDAP queries. If your LDAP domain is example.com this is usually
`dc=example,dc=com`, however you can fine tune this to be more specific for example to only include objects inside the
authelia OU: `ou=authelia,dc=example,dc=com`. This is prefixed with the [additional_users_dn](#additional_users_dn) for
user searches and [additional_groups_dn](#additional_groups_dn) for groups searches.
### username_attribute
type: string
{: .label .label-config .label-purple }
required: no
{: .label .label-config .label-green }
The LDAP attribute that maps to the username in Authelia. The default value is dependent on the [implementation](#implementation),
refer to the [attribute defaults](#attribute-defaults) for more information.
### additional_users_dn
type: string
{: .label .label-config .label-purple }
required: no
{: .label .label-config .label-green }
Additional LDAP path to append to the [base_dn](#base_dn) when searching for users. Useful if you want to restrict
exactly which OU to get users from for either security or performance reasons. For example setting it to
`ou=users,ou=people` with a base_dn set to `dc=example,dc=com` will mean user searches will occur in
`ou=users,ou=people,dc=example,dc=com`. The default value is dependent on the [implementation](#implementation), refer
to the [attribute defaults](#attribute-defaults) for more information.
### users_filter
type: string
{: .label .label-config .label-purple }
required: no
{: .label .label-config .label-green }
The LDAP filter to narrow down which users are valid. This is important to set correctly as to exclude disabled users.
The default value is dependent on the [implementation](#implementation), refer to the
[attribute defaults](#attribute-defaults) for more information.
### additional_groups_dn
Similar to [additional_users_dn](#additional_users_dn) but it applies to group searches.
### groups_filter
Similar to [users_filter](#users_filter) but it applies to group searches.
### mail_attribute
The attribute to retrieve which contains the users email addresses. This is important for the device registration and
password reset processes.
The user must have an email address in order for Authelia to perform
identity verification when a user attempts to reset their password or
register a second factor device.
### display_name_attribute
The attribute to retrieve which is shown on the Web UI to the user when they log in.
### user
The distinguished name of the user paired with the password to bind with for lookup and password change operations.
### password
The password of the user paired with the user to bind with for lookup and password change operations.
Can also be defined using a [secret](../secrets.md) which is the recommended for containerized deployments.
## Implementation Guide
There are currently two implementations, `custom` and `activedirectory`. The `activedirectory` implementation
must be used if you wish to allow users to change or reset their password as Active Directory
uses a custom attribute for this, and an input format other implementations do not use. The long term
intention of this is to have logical defaults for various RFC implementations of LDAP.
### Defaults
The below tables describes the current attribute defaults for each implementation.
#### 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|
|:-------------:|:------------:|:----------:|:--:|:--------:|
|custom |n/a |displayname |mail|cn |
|activedirectory|sAMAccountName|displayname |mail|cn |
#### Filter defaults
The filters are probably the most important part to get correct when setting up LDAP.
You want to exclude disabled accounts. The active directory example has two attribute
filters that accomplish this as an example (more examples would be appreciated). The
userAccountControl filter checks that the account is not disabled and the pwdLastSet
makes sure that value is not 0 which means the password requires changing at the next login.
|Implementation |Users Filter |Groups Filter|
|:-------------:|:------------:|:-----------:|
|custom |n/a |n/a |
|activedirectory|(&(|({username_attribute}={input})({mail_attribute}={input}))(objectCategory=person)(objectClass=user)(!userAccountControl:1.2.840.113556.1.4.803:=2)(!pwdLastSet=0))|(&(member={dn})(objectClass=group)(objectCategory=group))|
## Refresh Interval
This setting takes a [duration notation](../index.md#duration-notation-format) that sets the max frequency
for how often Authelia contacts the backend to verify the user still exists and that the groups stored
in the session are up to date. This allows us to destroy sessions when the user no longer matches the
user_filter, or deny access to resources as they are removed from groups.
In addition to the duration notation, you may provide the value `always` or `disable`. Setting to `always`
is the same as setting it to 0 which will refresh on every request, `disable` turns the feature off, which is
not recommended. This completely prevents Authelia from refreshing this information, and it would only be
refreshed when the user session gets destroyed by other means like inactivity, session expiration or logging
out and in.
This value can be any value including 0, setting it to 0 would automatically refresh the session on
every single request. This means Authelia will have to contact the LDAP backend every time an element
on a page loads which could be substantially costly. It's a trade-off between load and security that
you should adapt according to your own security policy.
## Important notes
Users must be uniquely identified by an attribute, this attribute must obviously contain a single value and
be guaranteed by the administrator to be unique. If multiple users have the same value, Authelia will simply
fail authenticating the user and display an error message in the logs.
In order to avoid such problems, we highly recommended you follow https://www.ietf.org/rfc/rfc2307.txt by using
`sAMAccountName` for Active Directory and `uid` for other implementations as the attribute holding the
unique identifier for your users.
As of versions > `4.24.0` the `users_filter` must include the `username_attribute` placeholder, not including this will
result in Authelia throwing an error.
In versions <= `4.24.0` not including the `username_attribute` placeholder will cause issues with the session refresh
and will result in session resets when the refresh interval has expired, default of 5 minutes.