Fixes and optimisations for the Murfey authentication API

[tieneupin]

Changes:

• Forwards only essential headers to the auth server to prevent timeouts due to mismatch between header, body, and methods.
• Migrate authentication server querying logic out into a helper function to minimise repetition.

In PR #728 , we introduced logic to forward ALL headers from the incoming requests to the authentication server to support the implementation of local decrypting and parsing of incoming requests without the need to repeatedly query an OAuth2 /userinfo endpoint.

However, it looks like there are headers used by the API endpoint to verify the incoming request, and if a mismatch is found, the request will time out. For example, a POST request sent by the frontend will have its headers forwarded to the authentication server as part of a GET request, and the presence of some headers from the original POST request causes the subsequent GET request to timeout. Fixing this involved amending the logic to forward only the headers that are needed by the authentication server for local decryption and parsing of the request.

Additionally, some duplicated logic was observed in how the validation functions submit requests to the authentication server, so these have been migrated into a helper function that they can call.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.46%. Comparing base (467c2d0) to head (3dd9720).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #730      +/-   ##
==========================================
+ Coverage   46.07%   46.46%   +0.39%     
==========================================
  Files          91       91              
  Lines        9641     9631      -10     
  Branches     1261     1261              
==========================================
+ Hits         4442     4475      +33     
+ Misses       4979     4943      -36     
+ Partials      220      213       -7     

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