admission: only post requests are handled and return correctly

Signed-off-by: Christopher M. Luciano <cmluciano@us.ibm.com>

pkg/admission/server.go

@@ -35,6 +35,11 @@ func log500(w http.ResponseWriter, err error) {
 // ServeHTTP parses AdmissionReview requests and responds back
 // with the validation result of the entity.
 func ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		klog.Errorf("webhook cannot handle %s method", r.Method)
+		http.Error(w, fmt.Sprintf("invalid method %s, only POST requests are allowed", r.Method), http.StatusMethodNotAllowed)
+	}
 	if r.Body == nil {
 		klog.Errorf("received request with empty body")
 		http.Error(w, "admission review object is missing",
@@ -64,6 +69,7 @@ func ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		log500(w,err)
 	}
+	return
 }
 
 var (
@@ -72,11 +78,6 @@ var (
 		Version:  v1alpha1.SchemeGroupVersion.Version,
 		Resource: "httproutes",
 	}
-	gateway = meta.GroupVersionResource{
-		Group:    v1alpha1.SchemeGroupVersion.Group,
-		Version:  v1alpha1.SchemeGroupVersion.Version,
-		Resource: "gateway",
-	}
 )
 
 func routesEqual(new v1alpha1.HTTPRoute, old v1alpha1.HTTPRoute) bool {