feature to toggle off pkce

[satanshiro]

Closes/fixes #issue
#895

Checklist

• This PR makes changes to the public API
• I have included links for closing relevant issue numbers

[satanshiro]

Please let me know what to change I'll add tests as you see fit, once you think this is ok.
the tests are Passing
but one test that is not relevant with current solution

[codecov]

Codecov Report

Base: 77.69% // Head: 77.66% // Decreases project coverage by -0.03% ⚠️

Coverage data is based on head (c995c28) compared to base (f55517e).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #897      +/-   ##
==========================================
- Coverage   77.69%   77.66%   -0.03%     
==========================================
  Files          44       44              
  Lines        1690     1688       -2     
  Branches      331      330       -1     
==========================================
- Hits         1313     1311       -2     
  Misses        340      340              
  Partials       37       37              

Flag	Coverage Δ
unittests	77.66% <100.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/OidcClient.ts	93.22% <ø> (ø)
src/ResponseValidator.ts	90.47% <ø> (-0.15%)	⬇️
src/SigninRequest.ts	100.00% <ø> (ø)
src/TokenClient.ts	96.15% <ø> (-0.08%)	⬇️
src/OidcClientSettings.ts	92.30% <100.00%> (+0.24%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[pamapa]

thanks for contributing