ASP.NET - Signin with Google plus using Google Plus API - Part 2

ASP.NET - Signin with Google plus using Google Plus API - Part 2

In this post, we are going to use clientId obtained from google API console and create an signin page to use user's google plus email. Lets first create few basic classes which we can use to deserialize the JSON responses we get from google api calls.

Classes to hold deserialized JSON data from Google Plus

public class GoogleEmail
    public Data data { get; set; }

public class Data
    public string email { get; set; }

Login page to show Google+ Login button

This page holds the Google Plus Sign In button, clicking on which user will be presented with Google Plus Signin dialog screen.

  • In Head section of this page place the reference of plusone api javascript file.
  • Inside body place the button with google+ client api attributes. Be sure to use your Application ClientId for the data-clientid attribute.
  • Javascript function to handle the SignIn callback we get as a result from Google+ signin dialog. If user authenticates with google+ successfully, we will get an Access Token. We pass this access token to our second page.
    <script type="text/javascript">
        (function () {
            var po = document.createElement('script');
            po.type = 'text/javascript'; po.async = true;
            po.src = '';
            var s = document.getElementsByTagName('script')[0];
            s.parentNode.insertBefore(po, s);
    <div id="gConnect">
        <button class="g-signin" 
            data-scope=" "
            data-clientid="[YOUR APPLICATION CLIENT ID HERE]"
    <script type="text/javascript">
        * Calls the helper method that handles the authentication flow.
        * @param {Object} authResult An Object which contains the access token and
        *   other authentication information.
        function onSignInCallback(authResult) {
            if (authResult['access_token']) {
                // The user is signed in
                var loc = '/callback.aspx?accessToken=' + authResult['access_token'];
                window.location.href = loc;
            } else if (authResult['error']) {
                // There was an error, which means the user is not signed in.
                // As an example, you can troubleshoot by writing to the console:
                alert('There was an error: ' + authResult['error']);
            //console.log('authResult', authResult);

Code for callback.aspx

As we passed the access token from the first page in query string, we can use that here to make an API call to Google+ userinfo/email method to retrieve the user's email address. Using JavaScript Serializer class we can deserialize the json string into the .net classes we created in first step.

public partial class callback : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
        if (string.IsNullOrEmpty(Request.QueryString["access_token"])) return; 

        //let's send an http-request to Google+ API using the token           
        string json = GetGoogleUserJSON(Request.QueryString["access_token"]);

        //and Deserialize the JSON response
        JavaScriptSerializer js = new JavaScriptSerializer();
        GoogleEmail oUser = js.Deserialize<GoogleEmail>(json);

        if (oUser != null)
            Response.Write("Welcome, " +;

    /// <summary>
    /// sends http-request to Google+ API and returns the response string
    /// </summary>
    private string GetGoogleUserJSON(string access_token)
        string url = "";

        WebClient wc = new WebClient();
        wc.Headers.Add("Authorization", "OAuth " + Request.QueryString["accessToken"]);
        Stream data = wc.OpenRead(url);
        StreamReader reader = new StreamReader(data);
        string retirnedJson = reader.ReadToEnd();

        return retirnedJson;

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