1. Instead of 'realm_name' and 'password' the module gets
'project_name' and 'api_key' respectively.
2. Dictionary with 'auth_token' key should be returned, not
just a string with a token.
3. Client secret is an optional parameter and shouldn't be
required during authentication.
Closes-bug: #1719560
Change-Id: I886480b9aaec8493039ff83e114b8183a0f5fddc