fix: Make sure Okta iss has proper form

[scott-codecov]

Purpose/Motivation

Validate user input before using it as part of a redirect.

Fixes https://github.com/codecov/codecov-api/security/code-scanning/9

Links to relevant tickets

https://github.com/codecov/internal-issues/issues/67

What does this PR do?

Ensures that the Okta iss is of the form https://<subdomain>.okta.com

[codecov-public-qa]

Codecov Report

Merging #190 (59f00de) into main (576edd4) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #190   +/-   ##
=======================================
  Coverage   95.61%   95.62%           
=======================================
  Files         600      600           
  Lines       15204    15208    +4     
=======================================
+ Hits        14538    14542    +4     
  Misses        666      666           

Flag	Coverage Δ
unit	95.62% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	95.62% <100.00%> (+<0.01%)	⬆️

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

Files	Coverage Δ
codecov_auth/views/okta.py	100.00% <100.00%> (ø)

[codecov]

Codecov Report

Merging #190 (0b62de1) into main (576edd4) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 0b62de1 differs from pull request most recent head 59f00de. Consider uploading reports for the commit 59f00de to get more accurate results

@@          Coverage Diff          @@
##            main    #190   +/-   ##
=====================================
  Coverage   95.52   95.52           
=====================================
  Files        714     714           
  Lines      15610   15612    +2     
=====================================
+ Hits       14910   14912    +2     
  Misses       700     700           

Flag	Coverage Δ
unit	95.62% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	95.62% <100.00%> (+<0.01%)	⬆️

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

Files	Coverage Δ
codecov_auth/views/okta.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[codecov-qa]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (576edd4) 95.61% compared to head (59f00de) 95.62%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #190   +/-   ##
=======================================
  Coverage   95.61%   95.62%           
=======================================
  Files         600      600           
  Lines       15204    15208    +4     
=======================================
+ Hits        14538    14542    +4     
  Misses        666      666           

Flag	Coverage Δ
unit	95.62% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	95.62% <100.00%> (+<0.01%)	⬆️

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

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