[HIGH LEVEL] Update parseAuth method so auth guards to handle error not method

[eleanorreem]

• the Unauthorized Exceptioin wrapper was adding filler that was confusing the auth guards.
• Errors that are thrown are now handled by the auth guard rather than the auth service method. In general we want the controllers and auth guards to put wrappers around the exception and then for the nested methods to pass the error back

[Zahra-8d]

Question: Why do we have two separate variables for uid and userUid? Not gonna cause any issues but might be redundant.

[eleanorreem]

Different ways of doing it really. Userid and uid are the same thing - I just was using a mutable variable as uid isn't accessible outside the try catch. Any suggestions for a better pattern is welcome