func NewCookieSigner(key []byte) CookieSigner {
	return CookieSigner{signer: hmac.New(sha256.New, key)}
}
func NewCookieSigner(key []byte) CookieSigner {
	return CookieSigner{signer: hmac.New(sha256.New, key)}
}
// NewCookieSigner returns a new CookieSigner using the given key