Add JWKS parameters for verifying web token signatures

[michael-doubez]

Activate verification of token signature. Fix #89

Testing done

Submitter checklist

Preview Give feedback

1. Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
2. Ensure that the pull request title represents the desired changelog entry
3. Please describe what you did
4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[codecov]

Codecov Report

Attention: Patch coverage is 67.24138% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 73.27%. Comparing base (c3d9244) to head (9442607).
Report is 12 commits behind head on master.

Files	Patch %	Lines
...va/org/jenkinsci/plugins/oic/OicSecurityRealm.java	57.89%	10 Missing and 6 partials ⚠️
...jenkinsci/plugins/oic/OicJsonWebTokenVerifier.java	85.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #297      +/-   ##
============================================
+ Coverage     73.16%   73.27%   +0.11%     
- Complexity      189      209      +20     
============================================
  Files             9       10       +1     
  Lines           775      872      +97     
  Branches        113      123      +10     
============================================
+ Hits            567      639      +72     
- Misses          151      170      +19     
- Partials         57       63       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.