fix preflight requests

Signed-off-by: Jörn Friedrich Dreyer <jfd@butonic.de>

services/proxy/pkg/middleware/authentication.go

@@ -52,7 +52,7 @@ func Authentication(auths []Authenticator, opts ...Option) func(next http.Handle
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			ri := router.ContextRoutingInfo(r.Context())
-			if isOIDCTokenAuth(r) || ri.IsRouteUnprotected() {
+			if isOIDCTokenAuth(r) || ri.IsRouteUnprotected() || r.Method == "OPTIONS" {
 				// Either this is a request that does not need any authentication or
 				// the authentication for this request is handled by the IdP.
 				next.ServeHTTP(w, r)