IdentityService Task/Class

I created a new task in AuthenticationClient that provides a call out to the Identity Service. Also, I noticed that there was already a model in Common for an IdentityResponse. I created a simple class to serialize the JSON payload into with the new task in AuthenticationClient.

I'm very new to this toolkit, but I'm seeing great potential, and a lot of places for improvement that I would be happy to help with. I'm also very new to contributing on GitHub so please be gentile!!