adding oidc desired username as option in config

[Lite5h4dow]

This PR allows people to use their desired username from their oidc provider instead of their email address. this is a user-facing feature and doesn't change any underlying processes

• have read the CONTRIBUTING.md file
• raised a GitHub issue or discussed it on the projects chat beforehand
• added unit tests
• added integration tests
• updated documentation if needed
• updated CHANGELOG.md

[kradalby]

Hi, please fix the last checkboxes in the pr and add a justification for the feature, it seems like a linked issue is also missing

[Lite5h4dow]

related issues:

• [Feature] OIDC DisplayName and ProfilePicURL support #1980
• Option to use Username instead of email when logging in via oidc #938

I did discuss this In the discord last year some time, and again earlier this week, but decided to just make a pr.

[Lite5h4dow]

This PR makes a simple adjustment to the username discernment process when using OIDC, we already pulled in the desired_username from the token, we just needed to clean it up and use it.

[Lite5h4dow]

is it just me or is there currently no support for profile images? if not that might be what I add next. i just don't know where we would need to put it so the tailscale client could pick it up (this would only really be a feature for android, windows and mac clients, I don't believe the linux client has a front end, its all cli.

[ChibangLW]

Maybe have a look at #1934. It is a more general improvement which also results in usable preferred_username.

As well as #1981, which adds profile picture support.

I am not sure whats the maintainers stand on these PRs and in general on additional OIDC features.

[Lite5h4dow]

well if your gonna support OIDC, why half arse it?