AccessToken missing id_toek in jsonSerialize

[fanglingsu]

I think it would be better to add the id_token also to the response of the jsonSerialize Method of the access Token. So the received, token containing the id token, could be stored in the session. Maybe you can add something like this to the AccessToken class:

public function jsonSerialize()
{
    $parameters = parent::jsonSerialize();
    if ($this->idToken) {
        $parameters['id_token'] = (string)$this->idToken;
    }

    return $parameters;
}

[steverhoades]

@fanglingsu This looks good. Can you provide a pull request?

[fanglingsu]

I don't have much time, so you can put it in.