t.Errorf("Unexpected location, expected = %s, found = `%s`", rec.Header().Get("Location"), expectedLocation)
	}
}

// postPresignSignatureV4 - presigned signature for PostPolicy requests.
func postPresignSignatureV4(policyBase64 string, t time.Time, secretAccessKey, location string) string {
	// Get signining key.
	signingkey := getSigningKey(secretAccessKey, t, location, "s3")