Today we have to see Asp.Net MVC3 Razor with facebook Authentication before we see details first u have to Register u r Application in facebook developer(https://developers.facebook.com/apps).and u got AppID.

Ok now lets see step by step

Step 1 :Open VS 2010 go to project and select Asp.Net MVC 3 Web Application

Step 2 :select empty and select Razor

Step 3 :Now go to Controllers and right click and give Some name like Home Controllers and add this code

public ActionResult Index()
{
if (!string.IsNullOrEmpty(Request.Params["signed_request"]))
{
ViewBag.IsAuthenticated =true;
Dictionary<string,string> info = Utility.DecodePayload(Request.Params["signed_request"]);
Session["access_token"] = info;
Facebook.FacebookAPI api = new Facebook.FacebookAPI(info["oauth_token"]);
var json = api.Get("/me");
}
 else
ViewBag.IsAuthenticated = false;
return View();
}

Step 4 :Now go to Model and

create utility class(Here u have to Add Facebook API throw reference in our App)

public class Utility
{
public static Dictionary<string, string> DecodePayload(string payload)
{
var parameters = new Dictionary<string, string>();

 try
{
string[] sB64String = payload.Split('.');
payload = payload.Replace((sB64String[0] + "."), string.Empty);
 //End
var encoding = new UTF8Encoding();
var decodedJson = payload.Replace("=", string.Empty).Replace('-', '+').Replace('_', '/');
var base64JsonArray = Convert.FromBase64String(decodedJson.PadRight(decodedJson.Length + (4 -
decodedJson.Length % 4) % 4, '='))

var json = encoding.GetString(base64JsonArray);

var jObject = JSONObject.CreateFromString(json);
 //parameters.Add("liked", jObject.Dictionary["page"].Dictionary["liked"].Boolean.ToString());
{
parameters.Add("isAuthorized", "true");
parameters.Add("oauth_token", jObject.Dictionary["oauth_token"].String);
parameters.Add("profile_id", jObject.Dictionary["user_id"].String);
}
 else
{
parameters.Add("isAuthorized", "false");
parameters.Add("oauth_token", string.Empty);
}

}
catch { }

return parameters;
}
}

Step 5 :now go to Home Controllers and right click on Index and add View after adding u have to write this code

index.chtml code is

<html xmlns:fb="http://www.facebook.com/2008/fbml">
<body>
<script src="http://connect.facebook.net/en_US/all.js"></script>

<div id="fb-root">

</div>
<script>

// assume we are already logged in
FB.init({ appId: '161729093918865', xfbml: true, cookie: true, oauth: true });

if ([email protected]().ToLower())

{
window.top.location = "http://www.facebook.com/connect/uiserver.php"
+ "?app_id=" + '161729093918865'
+ "&next=" + 'http://apps.facebook.com/spatialidea/'
+ "&display=page"
+ "&cancel_url=" + 'http://www.facebook.com/'
+ "&locale=en_IN"
+ "&perms=publish_stream,email&method=permissions.request"
+ "&return_session=1&session_version=3&fbconnect=0&canvas=1&legacy_return=1";
}
</script>
</body>
</html>

Step 6 : Now run the App