Fix AuthErrorHandler behavior and improve validation logic

[moutonjeremy]

Ensure that the AuthErrorHandler does not disable validation or OpenAPI documentation when set alone. Update the logic for restoring defaults in the New function to account for cases where only error handlers are configured. Additionally, clarify the AuthErrorHandler comment to include 5xx errors in its configuration.

[Copilot]

Pull request overview

This PR adjusts config merging in New() so that configuring only AuthErrorHandler (or only handler functions) doesn’t inadvertently disable default request validation and OpenAPI docs, and updates related comments/tests.

Changes:

• Update New() config-merging “restore defaults” logic to treat AuthErrorHandler similar to ValidationErrorHandler.
• Clarify AuthErrorHandler field comment to note it may handle 5xx AuthError responses.
• Add a regression test ensuring AuthErrorHandler-only config preserves default validation and docs routes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
types.go	Updates AuthErrorHandler comment to include 5xx cases.
fiberoapi.go	Adjusts default-restoration heuristic when only handlers are configured.
custom_validation_error_test.go	Adds test ensuring AuthErrorHandler alone doesn’t disable defaults.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.