Support custom start URL search parameters in OIDC provider

[chriskilding-relx]

Hey, I just made a Pull Request!

Allow the Backstage admin to define custom OIDC start URL search (query) parameters for the OIDC authentication provider.

This is done by defining the startUrlSearchParameters property in the Backstage YAML config.

Implements #30754

:heavy_check_mark: Checklist

• [ ] A changeset describing the change and affected packages. (more info)
• [x] Added or updated documentation
• [x] Tests for new functionality and regression tests for bug fixes
• [ ] Screenshots attached (for UI changes)
• [ ] All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie[bot]]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage/plugin-auth-backend-module-oidc-provider	plugins/auth-backend-module-oidc-provider	patch	v0.4.10

[backstage-goalie[bot]]

Thanks for the contribution! All commits need to be DCO signed before they are reviewed. Please refer to the the DCO section in CONTRIBUTING.md or the DCO status for more info.

[chriskilding-relx]

@Rugvip I see I need to sign the commit (after I've squashed them into one of course) with a DCO. Do I have to use a real company email address for this, or can I use the GitHub noreply address which is normally associated with my commits instead?

[chriskilding-relx]

@Rugvip hey, is anything else needed to get this PR over the finish line?

[chriskilding-relx]

@Rugvip @freben thanks for merging the associated docs PR - please could this be reviewed and merged?

[freben]

Note the warning above - you need to add a changeset to the PR.

[chriskilding-relx]

@freben thanks, I've now added a changeset to the PR. Hopefully it's good to go now?

[github-actions[bot]]

Thank you for contributing to Backstage! The changes in this pull request will be part of the 1.47.0 release, scheduled for Tue, 20 Jan 2026.