Authenticate a user against an LDAP directory
Useful for Windows Active Directory and other LDAP-based organisations
to maintain a single password across the organisation.

Optionally authenticates only if a member of a given group in the directory.

The person must have registered with Friendika using the normal registration 
procedures in order to have a Friendika user record, contact, and profile.

Note when using with Windows Active Directory: you may need to set TLS_CACERT in your site
ldap.conf file to the signing cert for your LDAP server. 

The required configuration options for this module may be set in the .htconfig.php file
e.g.:

$a->config['ldapauth']['ldap_server'] = 'host.example.com';
...etc.
