Allow POST method to request service/token in readonly mode

[stonezdj]

fixes #18243

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Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

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[codecov]

Codecov Report

Merging #19556 (c5d0f82) into main (f6d5bf2) will decrease coverage by 22.23%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main   #19556       +/-   ##
===========================================
- Coverage   67.53%   45.30%   -22.23%     
===========================================
  Files         990      244      -746     
  Lines      109021    13318    -95703     
  Branches     2719     2719               
===========================================
- Hits        73629     6034    -67595     
+ Misses      31426     6983    -24443     
+ Partials     3966      301     -3665     

Flag	Coverage Δ
unittests	45.30% <ø> (-22.23%)	⬇️

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see 750 files with indirect coverage changes

[chlins]

lgtm