External LDAP auth plugin. Env variables are used for configuring - see example systemd service 'mongooseim.service'.
The following env variables are mandatory:
LDAP_SERVER - ldap server address
LDAP_PORT - ldap port
LDAP_BASEDN - ldap basedn (dc=example,dc=org')
The following env variables are optional:
LDAP_MEMBEROF
LDAP_SECURECONN - use ldaps or not (true/false)
LDAP_CHECKPWEXPIRED - check for password expiration via ldap attribute 'krbPasswordExpiration' (true/false)
Users with expired passwords (krbPasswordExpiration value < time.Now) can't login. Useful for freeIPA users.