feat: save pkce code verifier/challenge for debugging

[csmig]

In oidcProvider.js, persist to localStorage the values of the last used PKCE code_verifier and code_challenge. This might help in debugging esoteric issues as reported in #1440.

The last used values can be found using DevTools or a JS console to view localStorage items last-code-verifier and last-code-challenge. The last-code-challenge should be the URL encoded Base64 representation of the SHA256 digest of last-code-verifier.

In a Linux shell, the proper code challenge for a given last-code-verifier can be calculated by invoking:

echo -n "<last-code-verifier>" | sha256sum | xxd -r -p | base64 | tr '+/' '-_' | tr -d '='

[sonarqubecloud]

Quality Gate passed for 'nuwcdivnpt_stig-manager-client'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[csmig]

Replaced by #1456