Properly handle ldap3.abstract.attribute.Attribute value

This commit fixes an issue created on commit 2e7a01f30adb5e641805f2c37921d111f955f31d.

Ldap object is type <class 'ldap3.abstract.attribute.Attribute'>.
So we need to return the value and verify if it's null, string or list.

Fixes #12813

backend/open_webui/routers/auths.py

@@ -230,7 +230,7 @@ async def ldap_auth(request: Request, response: Response, form_data: LdapForm):
 
         entry = connection_app.entries[0]
         username = str(entry[f"{LDAP_ATTRIBUTE_FOR_USERNAME}"]).lower()
-        email = entry[f"{LDAP_ATTRIBUTE_FOR_MAIL}"]
+        email = entry[f"{LDAP_ATTRIBUTE_FOR_MAIL}"].value # retrive the Attribute value
         if not email:
             raise HTTPException(400, "User does not have a valid email address.")
         elif isinstance(email, str):