backend: auth: Extract RefreshAndSetToken from headlamp.go

[skoeva]

This change extracts the RefreshAndSetToken function from headlamp.go into the auth package.

Part of:

• backend: Add auth package from headlamp.go OIDC functions #3482

Updates

• Add params struct to help move future functions
• Add comprehensive tests in auth_test.go

Testing

cd backend
go test -v ./pkg/auth -run RefreshAndSetToken

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[joaquimrocha]

Is there a chance (honest question) we could have the tests being done for the same logic, before the extraction commit. This way we could verify that everything keeps working whereas right now we are testing for the new changes already.

[Copilot]

Pull request overview

This PR extracts the OIDC token refresh-and-cookie-setting logic from HeadlampConfig into the shared auth package and adds focused tests around it. It supports the ongoing effort in #3482 to progressively move and test OIDC-related auth functionality.

Changes:

• Introduces auth.RefreshAndSetTokenParams and auth.RefreshAndSetToken, encapsulating token refresh, cookie update, and telemetry recording in the auth package.
• Replaces the old (*HeadlampConfig).refreshAndSetToken method with a call to the new auth.RefreshAndSetToken within OIDCTokenRefreshMiddleware.
• Adds comprehensive tests in auth_test.go for RefreshAndSetToken, including default ID token behavior, access token mode, and error handling (no cookie set on failure).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
backend/pkg/auth/auth.go	Adds RefreshAndSetTokenParams and RefreshAndSetToken, wiring together token refresh, cookie setting, and telemetry with configurable token type and issuer URL.
backend/pkg/auth/auth_test.go	Adds helpers and three tests validating that RefreshAndSetToken picks the correct token (ID vs access), sets the expected cookie, and avoids setting cookies on refresh errors.
backend/cmd/headlamp.go	Removes the HeadlampConfig.refreshAndSetToken method and switches OIDCTokenRefreshMiddleware to use the new auth.RefreshAndSetToken API while passing the existing config and telemetry fields.

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[skoeva]

There aren't any changes in the function logic so coupling the tests with the extracted code should be fine