auth-service.ts

private getToken(): Promise<string> {
  var token = localStorage.getItem(AUTHTOKEN_KEY);

  if (this.isExpired(token)) {
    // Token is expired, try to get new token if refresh_token is available
    var refreshToken = localStorage.getItem(REFRESHTOKEN_KEY);
    if (refreshToken) {
      return this.http.post(authConfig.loginUrl, $.param({
        'grant_type': 'refresh_token',
        'refresh_token': refreshToken,
      })).then(response => {
        localStorage.setItem(AUTHTOKEN_KEY, response.content[authConfig.tokenName]);
        localStorage.setItem(REFRESHTOKEN_KEY, response.content['refresh_token']);

        return response.content[authConfig.tokenName];
      }).catch(() => {
        // Error trying to refresh authentication token, log out user
        localStorage.removeItem(AUTHTOKEN_KEY);
        localStorage.removeItem(REFRESHTOKEN_KEY);
        this.userService.clear();

        return null;
      });
    }

    // No refresh token available, log out user
    localStorage.removeItem(AUTHTOKEN_KEY);
    this.userService.clear();

    return Promise.resolve(null);
  }

  return Promise.resolve(token);
}