Third party login, or Federated Identity, refers to a software system where a user's Identity Provider handles verifying the login, and assures a using application that the user is identified correctly.
This is seen in web applications all over as 'Login with Facebook', 'Login with Google', and others.
Your Rdbhost.com hosted app can use Third Party Login to login to your application. We have supported OpenID for a long time, and have now added OAuth based authentication.
Google dropped their support for OpenID2 recently, and forced us to start supporting the OAuth style. Google actually propounds the new OpenID Connect standard, but they seem to be the only big name that supports it, so we will wait and see, possibly supporting that in the future.
We have tested our Federated Identity processing with Google, Facebook and LinkedIn, who use OAuth2, and Twitter using OAuth1, as well as Yahoo with OpenID2.