fix: read OIDC Prompt from the Prompt key, not the Ports key (#12557)

[DeepDiver1975]

Summary

Fixes #12557.

AppConfig::loadOpenIdConfigFromSystemConfig() read the OpenID Connect Prompt value from OidcPortsKey instead of OidcPromptKey. As a result, an administrator-provided Prompt in the system configuration ([OpenIDConnect] section / Windows registry) was ignored, and prompt was instead populated with the raw Ports string (e.g. "8080,8443"), which is not a valid OIDC prompt parameter. Since a valid system OIDC config fully replaces the theme config, the configured prompt was unreachable.

Changes

• Read prompt from OidcPromptKey.
• Add a regression test (testLoadOpenIdConfig) that exercises loadOpenIdConfigFromSystemConfig() and asserts prompt, ports, and scopes are each sourced from their own key.
• Make loadOpenIdConfigFromSystemConfig() public (mirroring the existing configPath testing convention) so it is reachable from the test.
• Add changelog entry.

Testing

AppConfigTest passes locally (4 passed, 0 failed). The new test fails before the fix (prompt would equal "8080,8443") and passes after.

Note

#12560 backports the same fix to the 7.1 branch.

🤖 Generated with Claude Code

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[modSpike]

the tests should rely on the original public interfaces only - I do not agree to making any of the internal "helper" functions public as they should never be called by any impl - that is why they are private. This is basic encapsulation.

please refactor your new test to use the appconfig instance only, as that is what is and should continue to be used in real life.

you should be able to essentially do the same thing wrt setting up the test values in a fake system config, then check the values on a resulting appConfig instance.