Support negating for skip auth routes

[ianldgs]

Description

Allow negating a route on skip-auth-routes, using syntax !=.
It works for specific methods: GET!=path_regex and for all methods: !=path_regex.

Motivation and Context

In the project I work, we have a backend API in which only one entity should be authenticated. All the rest should not.
Instead of keeping an updated list of every API route that we have, it's much easier to allow anything but the specific entity.

E.g.:

skip_auth_routes = [
  "!=^/api/my-private-entity", # my-private-entity needs authentication, anything else will skip auth
]

How Has This Been Tested?

Wrote some unit tests, and I have a postman collection with tests for my project with oauth2-proxy in front.

Checklist:

• My change requires a change to the documentation or CHANGELOG.
• I have updated the documentation/CHANGELOG accordingly.
• I have created a feature (non-master) branch for my PR.

[JoelSpeed]

Golang sadly doesn't support negative lookaheads so I think what you're doing here is probably the best solution

[ianldgs]

Golang sadly doesn't support negative lookaheads so I think what you're doing here is probably the best solution

Yeah, I tried to use a package regexp2, which supports negative lookaheads, but then it could break patterns from existing projects.

[JoelSpeed]

Looks good, thanks!

[ianldgs]

Awesome! I believe I have fixed CI.