/**
   * Make a call to our backend with user credentials
   * Verify presence of JWT in the response's header
   * Store it in local storage and return true for a successful login or false to a failed one
   * @param {User} user
   * @returns {Observable<boolean>}
   */
  login(user: User): Observable<boolean> {
    return this.http.post('/api/login', JSON.stringify({ mail: user.mail, password: user.password }))
      .map(response => {
        // login successful if there's a jwt token in the response
        let token = response.headers.get('Authorization');
        if (token) {
          // set token property
          this.token = token;

          // store username and jwt token in local storage to keep user logged in between page refreshes
          localStorage.setItem('token', token);

          // return true to indicate successful login
          return true;
        } else {
          // return false to indicate failed login
          return false;
        }
      })
      .catch(AuthenticationService.handleError);
  }