Add a setting to override the username field

docs/settings.rst

@@ -21,7 +21,7 @@ Settings
    The root of the LDAP tree to search for user account information. The
    contents of this tree can be further refined using the filtering settings.
    This should be a string specifying the complete root path::
- 
+
       LDAP_SYNC_BASE = "OU=Users,DC=example,DC=com"
 
 .. attribute:: LDAP_SYNC_BASE_USER
@@ -73,6 +73,14 @@ Settings
           "mail": "email",
       }
 
+.. attribute:: LDAP_SYNC_USERNAME_FIELD
+
+   :default: ``None``
+
+   An optional field on the synchronized User model to use as the unique key for
+   each user. If not specified, the User model's ``USERNAME_FIELD`` will be used.
+   If specified, the field must be included in ``LDAP_SYNC_USER_ATTRIBUTES``.
+
 .. attribute:: LDAP_SYNC_GROUP_FILTER
 
    :default: ``""``

ldap_sync/management/commands/syncldap.py

@@ -54,7 +54,13 @@ def sync_ldap_users(self, ldap_users):
         """
         model = get_user_model()
         attributes = getattr(settings, 'LDAP_SYNC_USER_ATTRIBUTES', None)
-        username_field = getattr(model, 'USERNAME_FIELD', 'username')
+        username_field = getattr(settings, 'LDAP_SYNC_USERNAME_FIELD', None)
+        if username_field is None:
+            username_field = getattr(model, 'USERNAME_FIELD', 'username')
+
+        if not model._meta.get_field(username_field).unique:
+            error_msg = ("Username field '%s' must be unique" % username_field)
+            raise ImproperlyConfigured(error_msg)
 
         if username_field not in attributes.values():
             error_msg = ("LDAP_SYNC_USER_ATTRIBUTES must contain the "