fix: handle token hook auth config

[hperl]

The code that fetches the auth config for the token hook incorrectly assumed that koanf returns JSON, when instead it is a nested map[string]any. This code fixes that.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (22f0119) 76.01% compared to head (3ebd911) 76.01%.
Report is 3 commits behind head on master.

Files	Patch %	Lines
oauth2/token_hook.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3677   +/-   ##
=======================================
  Coverage   76.01%   76.01%           
=======================================
  Files         134      134           
  Lines       10077    10036   -41     
=======================================
- Hits         7660     7629   -31     
+ Misses       1905     1900    -5     
+ Partials      512      507    -5     

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