login(username: string, password: string): Observable<User> {

const body = { username: username, password: password };

const headers = new HttpHeaders();
headers.append("Authorization", "Basic " + btoa("username:password"));
headers.append("Content-Type", "application/x-www-form-urlencoded");

return this.http
  .post<User>(`${BASE_URL}/sign-in`, body, { headers: headers })
  .do(user => (this.user = user));
}