stripeHeaders(headers: Headers) {
    headers.append('Content-Type', 'application/x-www-form-urlencoded');
    headers.append('Authorization', 'Bearer ' + this.apiKey);
  }

  updateBilling(customerId, cardNumber, expiryMonth, expiryYear, cvc): Observable<any> {
    let headers = new Headers();
    this.stripeHeaders(headers);
    let jsonParams = {
      source: {
        object: 'card',
        number: cardNumber,
        exp_month: expiryMonth,
        exp_year: expiryYear,
        cvc: cvc
      }
    }
    let stringParams = 'source={"object":"card","number":' + cardNumber + ',"exp_month":' + expiryMonth + ',"exp_year":' + expiryYear + ',"cvc":' + cvc + '}';
    return this.http.post('https://api.stripe.com/v1/customers/' + customerId, body, { headers: headers } )
      .map(res => res.json());
  }