Some changes about test cases:
Because MiddlewareCORS will return early on OPTIONS request,
this middleware should only be used once at NewServer function.
Test cases should pass AllowOrigin config instead of adding
this middleware again.
A new test case was added to test CORS preflight request with
an authenticator. Preflight request should always return 200 OK
regardless of autentications.
Co-authored-by: yuudi <yuudi@users.noreply.github.com>