cleanup(auth): update retry loop

[harkamaljot]

What this PR does

• Modifies the authentication retry loop to consistently wrap and return a non-transient error.

Why this change is needed

• The previous implementation returned either transient or non-transient errors, forcing the GAX retry policy to have complex, special-case logic to handle them. As auth errors should never be retried from Gax layer.

Important Caveat

• This PR does not yet implement a default retry policy for the auth layer.
• As a result, clients without a custom retry policy we add a default retry policy with attempts equal to 1.

[coryan]

We already have this:

google-cloud-rust/src/gax/src/retry_policy.rs

Line 325 in aef399f

pub struct NeverRetry;

[harkamaljot]

We already have this:

google-cloud-rust/src/gax/src/retry_policy.rs

Line 325 in aef399f

pub struct NeverRetry;

Got it, thanks @coryan. In that case, I'm still unclear on the use case for NoRetryPolicy, since my goal is to retry on most errors while avoiding retries on authentication failure.

Is the expectation that our default policy handles this correctly (by not retrying auth errors), and that we should honor any custom policy a customer provides to Gax, even if it retries on everything?

[coryan]

We already have this:

google-cloud-rust/src/gax/src/retry_policy.rs

Line 325 in aef399f

pub struct NeverRetry;

Got it, thanks @coryan. In that case, I'm still unclear on the use case for NoRetryPolicy, since my goal is to retry on most errors while avoiding retries on authentication failure.

Then you need to change Aip194Strict.

Is the expectation that our default policy handles this correctly (by not retrying auth errors), and that we should honor any custom policy a customer provides to Gax, even if it retries on everything?

Yes.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.58%. Comparing base (0e5bd3d) to head (bed0e15).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/auth/src/retry.rs	91.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2706   +/-   ##
=======================================
  Coverage   95.58%   95.58%           
=======================================
  Files          93       93           
  Lines        4006     4010    +4     
=======================================
+ Hits         3829     3833    +4     
  Misses        177      177           

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