func isRequestPresignedSignatureV2(r *http.Request) bool {
	_, ok := r.Form[xhttp.AmzAccessKeyID]
	return ok
}

// Verify if request has AWS Post policy Signature Version '4'.
func isRequestPostPolicySignatureV4(r *http.Request) bool {
	mediaType, _, err := mime.ParseMediaType(r.Header.Get(xhttp.ContentType))
	if err != nil {
		return false
	}
	return mediaType == "multipart/form-data" && r.Method == http.MethodPost
}

			HandlerFunc(s3APIMiddleware(api.HeadBucketHandler))
		// PostPolicy
		router.Methods(http.MethodPost).
			MatcherFunc(func(r *http.Request, _ *mux.RouteMatch) bool {
				return isRequestPostPolicySignatureV4(r)
			}).
			HandlerFunc(s3APIMiddleware(api.PostPolicyBucketHandler, traceHdrsS3HFlag))
		// DeleteMultipleObjects
		router.Methods(http.MethodPost).

	authTypeCount := 0
	for _, hasValidAuth := range []func(*http.Request) bool{
		isRequestSignatureV2, isRequestPresignedSignatureV2,
		isRequestSignatureV4, isRequestPresignedSignatureV4,
		isRequestJWT, isRequestPostPolicySignatureV4,
	} {
		if hasValidAuth(r) {
			authTypeCount++
		}
	}
	return authTypeCount > 1
}

// requestValidityHandler validates all the incoming paths for
// any malicious requests.