[Hot fix] Allow pkce with client secret

[NakoGH]

Description

Summary

We are forced to allow pkce with client secret even if it does not comply tothe OIDC specs.
...

Issues/PR dependencies

Issues to be resolved

Required PRs

Changes Made

• ...
• ...

Additional Notes

Classification

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 🔨 Refactor (non-breaking change that neither fixes a bug nor adds a feature)
• 🔧 Infra CI/CD (changes to configs of workflows)
• 💥 BREAKING CHANGE (fix or feature that require a new minimal version of the front-end)
• 😶‍🌫️ No impact for the end-users

Impact & Scope

• Core functionality changes
• Single module changes
• Multiple modules changes
• Database migrations required
• Other: ...

Testing

• 1. Tested this locally
• 2. Added/modified tests that pass the CI (or tested in a downstream fork)
• 3. Tested in a deployed pre-prod
• 0. Untestable (exceptionally), will be tested in prod directly

Documentation

• Updated the docs accordingly :
• " Docstrings
• # Inline comments
• No documentation needed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.05%. Comparing base (2fd64c0) to head (0e08667).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1046      +/-   ##
==========================================
+ Coverage   85.04%   85.05%   +0.01%     
==========================================
  Files         219      219              
  Lines       16232    16229       -3     
==========================================
  Hits        13804    13804              
+ Misses       2428     2425       -3     

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