Allow empty path in redirect_url

[stonezdj]

Fix for redirect to other sites with OIDC login and empty redirect_url parameter see #20226

Comprehensive Summary of your change

Issue being fixed

Fixes #20226

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• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.29%. Comparing base (b7b8847) to head (216de7c).
Report is 116 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #20238       +/-   ##
===========================================
- Coverage   67.56%   45.29%   -22.27%     
===========================================
  Files         991      244      -747     
  Lines      109181    13345    -95836     
  Branches     2719     2724        +5     
===========================================
- Hits        73768     6045    -67723     
+ Misses      31449     6998    -24451     
+ Partials     3964      302     -3662     

Flag	Coverage Δ
unittests	45.29% <ø> (-22.27%)	⬇️

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see 1235 files with indirect coverage changes

[wy65701436]

lgtm