Drop skipperOauthOidc cookies in oauthOidc filter

[AndreasSko]

The skipperOauthOidc cookies are only intended for Skipper, so they don't need to be forwarded to the application.

With this PR we simply drop those cookies before forwarding the request. This will reduce the overall header size of requests.
The implementation is inspired by the oauthGrant filter

Closes #3459

[Copilot]

Pull Request Overview

This pull request removes the skipperOauthOidc cookies from requests before they are forwarded to reduce header size. Key changes include:

• Adding a new test assertion to ensure the cookie is dropped.
• Modifying the request processing in the oidc filter to remove cookies with a name matching the skipperOauthOidc pattern.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
filters/auth/oidc_test.go	Added assertion to verify that the skipperOauthOidc cookie is dropped.
filters/auth/oidc.go	Updated cookie processing to drop cookies with names starting with the skipperOauthOidc prefix.

Comments suppressed due to low confidence (2)

filters/auth/oidc.go:795

• [nitpick] Consider aligning the cookie name reference (f.cookiename) with the naming used in tests (oauthOidcCookieName) to ensure consistency across the codebase.

if strings.HasPrefix(cookie.Name, f.cookiename) {

filters/auth/oidc_test.go:867

• Verify that the oauthOidcCookieName used in the test matches the cookie name pattern applied in the oidc filter for consistency.

assert.NotContains(t, string(requestDump), oauthOidcCookieName, oauthOidcCookieName+" cookie should be dropped")

[AlexanderYastrebov]

@AndreasSko FYI, I am testing what Copilot review is capable of so I've requested a review from it.

[AndreasSko]

@AlexanderYastrebov thank you for the review! I adjusted the code 🙂
In the process I noticed a bug in the insecureCookieJar, which I fixed as well (1889ea3).

[AlexanderYastrebov]

This feels somehow related to #1965

[AndreasSko]

This feels somehow related to #1965

Yeah, true. Would you like me to adjust anything in the test?

[AlexanderYastrebov]

👍

[AlexanderYastrebov]

Thank you for improving Skipper.

[AlexanderYastrebov]

@AndreasSko Could you please squash and rebase on top of master and make proper commit message. PR description and title should match those of commit message - the reason is that we release each merge to master so commit message becomes release notes.

[AndreasSko]

Sure! Squashed and adjusted the commit message to match the PR description 🙂

[AlexanderYastrebov]

👍

[AndreasSko]

@AlexanderYastrebov @MustafaSaber any update on this one? We are very eager to use it soon 😁😊

[MustafaSaber]

👍