AngularJS - 如何在ajax调用之前等待Google令牌

Question

我不确定如何使用承诺等待谷歌返回id_token。然后我会使用该令牌发出ajax请求。目前，它只是在拥有令牌之前立即执行ajax请求。

<script>
function onSignIn(googleUser) {
    id_token = googleUser.getAuthResponse().id_token;
}

var app = angular.module('myApp', ['ngDialog']);

app.controller('directory_controller', function($scope, $q, $http, ngDialog) {
    $http({
        headers: { "Content-Type": "application/x-www-form-urlencoded" },
        url: "my_ajax.php",
        method: "POST",
        data: "gtoken=" + id_token
    })
    .then(function successCallback(response) {
        console.log("success");
        console.log(response);
    }),
    function(response) {
        console.log("failure");
        console.log(response);
    }
});
</script>

<div ng-app='myApp'>
<div ng-controller='directory_controller'> 
</div>
</div>

<div class="g-signin2" data-onsuccess="onSignIn" data-theme="dark"></div>