Replaced the plethora of inter winding access functions and inputs in SessionUtils with just 2 functions, that both accept the same type for the user (AuthResult):
guessRegistrarForUser: given an AuthResult, finds a registrar that they have access to. If none is found - a ForbiddenException is thrown.
getRegistrarForUser[Cached]: (maybe should be called getRegistrarOnBehalfOfUser?) given an AuthResult and a clientId, loads and returns the registrar ONLY IF the user has access to it. Otherwise throws a ForbiddenException.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=214630657
84a0ace2ea