Make example/server usable for tests

[muir]

This re-arranges the example server code so that is usable as a test server. This does complicate the code a bit which makes it less good as an example.

Closes #204

[codecov[bot]]

Codecov Report

Merging #205 (2d0c08f) into main (0e7949b) will decrease coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #205      +/-   ##
==========================================
- Coverage   12.47%   12.45%   -0.02%     
==========================================
  Files          41       41              
  Lines        3263     3267       +4     
==========================================
  Hits          407      407              
- Misses       2845     2849       +4     
  Partials       11       11              

Impacted Files	Coverage Δ
pkg/oidc/userinfo.go	39.62% <0.00%> (-0.51%)	:arrow_down:
pkg/oidc/introspection.go	0.00% <0.00%> (ø)

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[github-actions[bot]]

:tada: This PR is included in version 1.9.1 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: