code: func (o *OAuthSession) NewCaptcha() (string, error) {
  	// Build form for POST request.
  	v := url.Values{
  		"api_type": {"json"},
  	}
  
  	type captcha struct {
  		Json struct {
  			Errors [][]string
  			Data   struct {
  				Iden string
  			}
  		}
  	}
  	c := &captcha{}
  
  	err := o.postBody("https://oauth.reddit.com/api/new_captcha", v, c)
  	if err != nil {
  		return "", err
  	}
  	return c.Json.Data.Iden, nil
  }
docs: // NewCaptcha returns a string used to create CAPTCHA links for users.