User has account

Issue: the user experience presented to the user may be different if the user has an account at GS already. For example, if the user does not have an account at a given GS, the client may choose to show that GS as an option, the client would want to explain that the user will need to register at the GS before sending the user to the GS.

For efficiency and a good user experience, the query if the user has an account at the GS would be in the same call as the Grant Request.