hmac.go
func (hs *HmacSigner) Encode(obj interface{}) ([]byte, error) {
	return hs.alg.Encode(hs, obj)
}
func (hs *HmacSigner) Encode(obj interface{}) ([]byte, error) {
	return hs.alg.Encode(hs, obj)
}
// Encode serializes the JSON marshalable obj data as a JWT.