impl(auth): trust boundaries module

[alvarowolfx]

Towards #4186

[codecov]

Codecov Report

❌ Patch coverage is 55.08475% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.20%. Comparing base (4e3ff47) to head (e973459).

Files with missing lines	Patch %	Lines
src/auth/src/trust_boundary.rs	38.46%	48 Missing ⚠️
src/auth/src/credentials/external_account.rs	62.50%	3 Missing ⚠️
src/auth/src/credentials/mds.rs	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4346      +/-   ##
==========================================
- Coverage   94.85%   94.20%   -0.65%     
==========================================
  Files         188      189       +1     
  Lines        7227     7332     +105     
==========================================
+ Hits         6855     6907      +52     
- Misses        372      425      +53     

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