code: func (t *Token) SignedString(key interface{}) (string, error) {
  	var sig, sstr string
  	var err error
  	if sstr, err = t.SigningString(); err != nil {
  		return "", err
  	}
  	if sig, err = t.Method.Sign(sstr, key); err != nil {
  		return "", err
  	}
  	return strings.Join([]string{sstr, sig}, "."), nil
  }
docs: // Get the complete, signed token