Stop using blind exceptions

[itsoyou]

SYN-96

config.py is out of scope because of its ongoing refactoring from other pr.

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Note

Low Risk
Behavioral change is mainly which exceptions propagate during login; auth still fails closed by returning None, with narrower catch scopes reducing risk of hiding unexpected errors.

Overview
Replaces generic Exception raises and except Exception blocks with typed errors so configuration and OAuth login failures are easier to reason about and do not swallow unrelated bugs.

Claims validation introduces InvalidClaimsValidatorError (ValueError) for bad validator DSL definitions, and ClaimsMismatchError when JWT vs introspection claim sources disagree (via all_list_elems_are_equal_return_the_elem). token_authenticator OAuth flow now catches only ClaimsMismatchError and SynapseError for those paths instead of any exception.

HttpAuth parsing raises ValueError for unknown types and malformed input; parse_auth logs and re-raises only ValidationError, KeyError, IndexError, and ValueError. Tests expect ValueError for bad auth config.

config.py is intentionally unchanged (other PR).

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[codecov]

Codecov Report

❌ Patch coverage is 67.85714% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.76%. Comparing base (47a36a5) to head (32f937c).

Files with missing lines	Patch %	Lines
synapse_token_authenticator/token_authenticator.py	28.57%	5 Missing ⚠️
synapse_token_authenticator/claims_validator.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
+ Coverage   76.35%   76.76%   +0.40%     
==========================================
  Files           9        9              
  Lines         791      792       +1     
  Branches      146      146              
==========================================
+ Hits          604      608       +4     
+ Misses        131      128       -3     
  Partials       56       56              

Files with missing lines	Coverage Δ
synapse_token_authenticator/http_auth.py	100.00% <100.00%> (ø)
synapse_token_authenticator/utils.py	100.00% <100.00%> (ø)
synapse_token_authenticator/claims_validator.py	77.95% <20.00%> (+1.98%)	⬆️
synapse_token_authenticator/token_authenticator.py	71.84% <28.57%> (ø)

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