A service responsible for allowing secure authentication for a user between the admin and site applications.
This service generates a single use and time sensitive token for a user from the admin application. This token is sent
to the user and he must present it in a timely manner to the site application to associate his session as authenticated
from the admin applicaiton.
Returns a randomly generated String that the user can then include in a request from the site application to
associate his site session with an admin user.
If the rolesToContrib parameter is not null, the roles in that list will be added to the site user when the
token is claimed.