将cognitoUser.authenticateUser回调转换为observable

login(username: string, password: string): Observable<{ type: string, result: any }>{
  const authData = {
    Username: username,
    Password: password
  };
  const authDetails = new AuthenticationDetails(authData);
  const userData = {
    Username: username,
    Pool: userPool
  };
  this.cognitoUser = new CognitoUser(userData);
  return new Observable<{ type: string, result: any}>(obs => {
    this.cognitoUser.authenticateUser(authDetails, {
      onSuccess: (result: any) => {
        obs.next({ type: 'success', result: result });
        obs.complete();
      },
      onFailure: (error: any) => obs.error(error),
      newPasswordRequired: (userAttributes, requiredAttributes) => {
        obs.next({ type: 'newPasswordRequired', result: [userAttributes, requiredAttributes] });
        obs.complete();
      }
    });
  });
}