From https://gerrit.wikimedia.org/r/c/mediawiki/extensions/LDAPAuthentication2/+/698964
Added support for SSL client certificates
Now it is possible to use SSL client certificate auth, together with LDAP.
After the webserver authenticated and validated the client certificate,
a configurable field can be used as username for the LDAP authentication.
The username extracted from SSL client certificate is matched through the
LDAP routines and makes it possible to login passwordless. If this is not
prefered by the user, the password can be reeanbled as a second authorisation
rule. Also a complete auto login is possible, if a client certificate is
detected. This is configurable through LocalSettings.php. If the webserver
doesn't detect a client certificate a fallback to the default login is done.