New SLO shape improves compatibility + fix codecov uploads

[escherize]

Keycloak is a little more lenient than Microsoft Azure Active Directory (aka Microsoft Entra ID). So I've updated the shape to match the Entra ID docs. This shape of a SLO logout request works on both.

Tested with:

• [x] Azure AD
• [x] keycloak

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 75.00%. Comparing base (399a475) to head (98990c2).

:exclamation: Current head 98990c2 differs from pull request most recent head 9dc41d8. Consider uploading reports for the commit 9dc41d8 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
- Coverage   75.03%   75.00%   -0.04%     
==========================================
  Files          10       10              
  Lines         693      692       -1     
  Branches      101      101              
==========================================
- Hits          520      519       -1     
  Misses         72       72              
  Partials      101      101              

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