code: func (u *User) Encode() string {
  	values := url.Values{}
  
  	// add custom attributes
  	if u.Attrs != nil {
  		for key, val := range u.Attrs {
  			values.Set(key, val)
  		}
  	}
  
  	values.Set("id", u.Id)
  	values.Set("name", u.Name)
  	values.Set("email", u.Email)
  	values.Set("photo", u.Photo)
  	return values.Encode()
  }
docs: // Encode will encode a user as a URL query string.