Authentication & Authorization using OAuth 2.0 Providers with ASP.NET WebForms: Code from Blaize Stewart's video tutorial "OAuth 2.0 Up and Running" (requires subscription), modified to include Microsoft's Live Connect functionality. See related blog posting - http://mvark.blogspot.in/2014/01/how-to-implement-authentication.html

OAuthASPNETWebForms.cs

/* 
OAuthRedirectPage.aspx
==========================
    <div>
        <asp:Label ID="OAuthLabel" runat="server" Text="Label"></asp:Label>
    </div>

OAuthRedirectPage.aspx.cs
==========================
*/ 
using System;
using Newtonsoft.Json.Linq;
 
public partial class OAuthRedirectPage : System.Web.UI.Page
{
    string OAuthURL = "https://accounts.google.com/o/oauth2/auth";
    string OAuthTokenURL = "https://accounts.google.com/o/oauth2/token";
    string client_id = "your_app_client_id";
    string client_secret = "your_app_client_secret";
    string scope = "https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fuserinfo.profile";
    string redirect_uri = "http://example.com/OAuthRedirectPage.aspx";
    string serviceURL = "https://www.googleapis.com/oauth2/v3/userinfo";
 
    //string OAuthURL = "https://www.facebook.com/dialog/oauth";
    //string OAuthTokenURL = "https://graph.facebook.com/oauth/access_token";
    //string client_id = "your_app_client_id";
    //string client_secret = "your_app_client_secret";
    //string scope = "user_about_me";
    //string redirect_uri = "http://example.com/OAuthRedirectPage.aspx";
    //string serviceURL = "https://graph.facebook.com/me";
 
    //string OAuthURL = "https://login.live.com/oauth20_authorize.srf";
    //string OAuthTokenURL = "https://login.live.com/oauth20_token.srf";
    //string client_id = "your_app_client_id";
    //string client_secret = "your_app_client_secret";
    //string scope = "wl.basic";
    //string redirect_uri = "http://example.com/OAuthRedirectPage.aspx";
    //string serviceURL = "https://apis.live.net/v5.0/me";
 
    protected void Page_Load(object sender, EventArgs e)
    {
        OAuthLabel.Text = "OAuth Redirect Page";
 
        if (Request["code"] != null)
        { 
        
            //Build the form request from the parameters
            string formData="client_id="  + client_id +
                "&client_secret=" + client_secret +
                "&redirect_uri=" + redirect_uri +
                "&grant_type=authorization_code" +
                "&code=" + Request["code"];
 
            //Exchange code for access token
            System.Net.WebClient ExchangeWC = new System.Net.WebClient();
            ExchangeWC.Headers.Add("Content-Type","application/x-www-form-urlencoded");
            var Results = ExchangeWC.UploadString(new System.Uri(OAuthTokenURL), formData);
 
            //Extract token from the results
            string access_token = "";
            try
            {
                JObject TokenData = JObject.Parse(Results);
                access_token = TokenData["access_token"].ToString();
            }
            catch (Exception) //next try URL encoded data
            {
                string[] URLParts = Results.Split('&');
                foreach (string S in URLParts) //extract the code from the URL
                {
                    string[] param = S.Split('=');
                    if (param[0].Replace("?", "") == "access_token")
                    {
                        access_token = param[1];
                        break;
                    }
 
                }
            }     
                //Call a service with the token
                System.Net.WebClient ProfileWC = new System.Net.WebClient();
                ProfileWC.Headers.Add("Authorization", "Bearer " + access_token);
                Results = ProfileWC.DownloadString(new System.Uri(serviceURL));
 
                //Display the users name..
                JObject UserProfile = JObject.Parse(Results);
                OAuthLabel.Text = "Hello, " + UserProfile["name"].ToString() ;
         
        }
        else //no "code" detected, redirect to OAuth service
        {
            string URL = OAuthURL + "" +
                "?client_id=" + client_id +
                "&scope=" + scope +
                "&redirect_uri=" + redirect_uri +
                "&response_type=code";
 
            Response.Redirect(URL);
        }
    }
}