FacebookApplication.VerifyAuthentication(_httpContext, GenerateLocalCallbackUri()) return null on Facebook

Question

I've developed an mvc 5 application using nopcommerce and i use facebook login using External callback it was working but now it is not working and i can't find out actual problem. And using this below code

this.FacebookApplication.VerifyAuthentication(_httpContext, GenerateLocalCallbackUri());

and it's returning me always null and authentication status failed i searched on web an do every thing and followed that steps but still i can't login with facebook.

My code is like this in FacebookProviderAuthorizer.cs

private AuthorizeState VerifyAuthentication(string returnUrl)
{
   var authResult = DotNetOpenAuth.AspNet.Clients.FacebookApplication.VerifyAuthentication(_httpContext, GenerateLocalCallbackUri());

   if (authResult.IsSuccessful)
   {
   }
}

And then write Call back method

private Uri GenerateLocalCallbackUri()
{
    string url = string.Format("{0}plugins/externalauthFacebook/logincallback/", _webHelper.GetStoreLocation());
    return new Uri(url);            
}

Then generate service login url

private Uri GenerateServiceLoginUrl()
{
   //code copied from DotNetOpenAuth.AspNet.Clients.FacebookClient file
   var builder = new UriBuilder("https://www.facebook.com/dialog/oauth");
   var args = new Dictionary<string, string>();
   args.Add("client_id", _facebookExternalAuthSettings.ClientKeyIdentifier);
   args.Add("redirect_uri", GenerateLocalCallbackUri().AbsoluteUri);
   args.Add("response_type", "token");
   args.Add("scope", "email");
   AppendQueryArgs(builder, args);
   return builder.Uri;
}

Answer 1

We ran into this same issue on Monday, 3/27/2017, when Facebook discontinued support for their Graph API v2.2.

We are also using DotNetOpenAuth, which was originally installed via Nuget. The source code is available at the link below:

https://github.com/DotNetOpenAuth/DotNetOpenAuth

Specifically, we discovered that our code was utilizing the 4.3 branch which contains the source code for the DotNetOpenAuth.AspNet.DLL. Upon inspecting the source, we discovered the problem is with this snippet of code from DotNetOpenAuth.AspNet\Clients\OAuth2\FacebookClient.cs, located within the QueryAccessToken method:

using (WebClient client = new WebClient()) {
     string data = client.DownloadString(builder.Uri);
     if (string.IsNullOrEmpty(data)) {
          return null;
     }

     var parsedQueryString = HttpUtility.ParseQueryString(data);
     return parsedQueryString["access_token"];
}

The issue, specifically, is the ParseQueryString call. Starting with v2.3 of the API, the data is no longer returned as an HTML query string, but in standard JSON format.

To fix this, we created our own custom class inheriting OAuth2Client and imported most of the same code from FacebookClient.cs. We then replaced the above code snippet with code that parses the JSON response to extract the access_token, and returns that instead. You can see an example of how to do this in the same FacebookClient class, within the GetUserData method:

FacebookGraphData graphData;
var request =
    WebRequest.Create(
        "https://graph.facebook.com/me?access_token=" +
             MessagingUtilities.EscapeUriDataStringRfc3986(accessToken));
using (var response = request.GetResponse()) {
     using (var responseStream = response.GetResponseStream()) {
        graphData = JsonHelper.Deserialize<FacebookGraphData>(responseStream);
     }
}

The only other change was to register our custom class in place of the FacebookClient class so the OAuth callback uses it to handle the post from Facebook's API. Once we did this, everything worked smoothly again.

Answer 2

I have used the code shared by @Vishal and got the same working.

The main thing that we have to focus is to override the QueryAccessToken method to use json response.

protected override string QueryAccessToken(Uri returnUrl, string authorizationCode)
    {
        var uri = BuildUri(TokenEndpoint, new NameValueCollection
            {
                { "code", authorizationCode },
                { "client_id", _appId },
                { "client_secret", _appSecret },
                { "redirect_uri", returnUrl.GetLeftPart(UriPartial.Path) },
            });

        var webRequest = (HttpWebRequest)WebRequest.Create(uri);
        string accessToken = null;            
        HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();

        // handle response from FB 
        // this will not be a url with params like the first request to get the 'code'
        Encoding rEncoding = Encoding.GetEncoding(response.CharacterSet);

        using (StreamReader sr = new StreamReader(response.GetResponseStream(), rEncoding))
        {
            var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
            var jsonObject = serializer.DeserializeObject(sr.ReadToEnd());
            var jConvert = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(jsonObject));

            Dictionary<string, object> desirializedJsonObject = JsonConvert.DeserializeObject<Dictionary<string, object>>(jConvert.ToString());
            accessToken = desirializedJsonObject["access_token"].ToString();
        }
        return accessToken;
    }

Steps to achieve this: Step 1. What you have to do is add one file named FacebookClientOverride.cs(other than FacebookClient.cs)

Here is the code snippet of the whole file.

 using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Web;
using DotNetOpenAuth.AspNet.Clients;
using Newtonsoft.Json;

public class FacebookClient : OAuth2Client
{
    #region Constants and Fields

    /// <summary>
    /// The authorization endpoint.
    /// </summary>
    private const string AuthorizationEndpoint = "https://www.facebook.com/dialog/oauth";

    /// <summary>
    /// The token endpoint.
    /// </summary>
    private const string TokenEndpoint = "https://graph.facebook.com/oauth/access_token";

    /// <summary>
    /// The user info endpoint.
    /// </summary>
    private const string UserInfoEndpoint = "https://graph.facebook.com/me";

    /// <summary>
    /// The app id.
    /// </summary>
    private readonly string _appId;

    /// <summary>
    /// The app secret.
    /// </summary>
    private readonly string _appSecret;

    /// <summary>
    /// The requested scopes.
    /// </summary>
    private readonly string[] _requestedScopes;

    #endregion

    /// <summary>
    /// Creates a new Facebook OAuth2 client, requesting the default "email" scope.
    /// </summary>
    /// <param name="appId">The Facebook App Id</param>
    /// <param name="appSecret">The Facebook App Secret</param>
    public FacebookClient(string appId, string appSecret)
        : this(appId, appSecret, new[] { "email" }) { }

    /// <summary>
    /// Creates a new Facebook OAuth2 client.
    /// </summary>
    /// <param name="appId">The Facebook App Id</param>
    /// <param name="appSecret">The Facebook App Secret</param>
    /// <param name="requestedScopes">One or more requested scopes, passed without the base URI.</param>
    public FacebookClient(string appId, string appSecret, params string[] requestedScopes)
        : base("facebook")
    {
        if (string.IsNullOrWhiteSpace(appId))
            throw new ArgumentNullException("appId");

        if (string.IsNullOrWhiteSpace(appSecret))
            throw new ArgumentNullException("appSecret");

        if (requestedScopes == null)
            throw new ArgumentNullException("requestedScopes");

        if (requestedScopes.Length == 0)
            throw new ArgumentException("One or more scopes must be requested.", "requestedScopes");

        _appId = appId;
        _appSecret = appSecret;
        _requestedScopes = requestedScopes;
    }

    protected override Uri GetServiceLoginUrl(Uri returnUrl)
    {
        var state = string.IsNullOrEmpty(returnUrl.Query) ? string.Empty : returnUrl.Query.Substring(1);

        return BuildUri(AuthorizationEndpoint, new NameValueCollection
                {
                    { "client_id", _appId },
                    { "scope", string.Join(" ", _requestedScopes) },
                    { "redirect_uri", returnUrl.GetLeftPart(UriPartial.Path) },
                    { "state", state },
                });
    }

    protected override IDictionary<string, string> GetUserData(string accessToken)
    {
        var uri = BuildUri(UserInfoEndpoint, new NameValueCollection { { "access_token", accessToken } });

        var webRequest = (HttpWebRequest)WebRequest.Create(uri);

        using (var webResponse = webRequest.GetResponse())
        using (var stream = webResponse.GetResponseStream())
        {
            if (stream == null)
                return null;

            using (var textReader = new StreamReader(stream))
            {
                var json = textReader.ReadToEnd();
                var extraData = JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
                var data = extraData.ToDictionary(x => x.Key, x => x.Value.ToString());

                data.Add("picture", string.Format("https://graph.facebook.com/{0}/picture", data["id"]));

                return data;
            }
        }
    }

    protected override string QueryAccessToken(Uri returnUrl, string authorizationCode)
    {
        var uri = BuildUri(TokenEndpoint, new NameValueCollection
                {
                    { "code", authorizationCode },
                    { "client_id", _appId },
                    { "client_secret", _appSecret },
                    { "redirect_uri", returnUrl.GetLeftPart(UriPartial.Path) },
                });

        var webRequest = (HttpWebRequest)WebRequest.Create(uri);
        string accessToken = null;
        HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();

        // handle response from FB 
        // this will not be a url with params like the first request to get the 'code'
        Encoding rEncoding = Encoding.GetEncoding(response.CharacterSet);

        using (StreamReader sr = new StreamReader(response.GetResponseStream(), rEncoding))
        {
            var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
            var jsonObject = serializer.DeserializeObject(sr.ReadToEnd());
            var jConvert = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(jsonObject));

            Dictionary<string, object> desirializedJsonObject = JsonConvert.DeserializeObject<Dictionary<string, object>>(jConvert.ToString());
            accessToken = desirializedJsonObject["access_token"].ToString();
        }
        return accessToken;
    }

    private static Uri BuildUri(string baseUri, NameValueCollection queryParameters)
    {
        var keyValuePairs = queryParameters.AllKeys.Select(k => HttpUtility.UrlEncode(k) + "=" + HttpUtility.UrlEncode(queryParameters[k]));
        var qs = String.Join("&", keyValuePairs);

        var builder = new UriBuilder(baseUri) { Query = qs };
        return builder.Uri;
    }

    /// <summary>
    /// Facebook works best when return data be packed into a "state" parameter.
    /// This should be called before verifying the request, so that the url is rewritten to support this.
    /// </summary>
    public static void RewriteRequest()
    {
        var ctx = HttpContext.Current;

        var stateString = HttpUtility.UrlDecode(ctx.Request.QueryString["state"]);
        if (stateString == null || !stateString.Contains("__provider__=facebook"))
            return;

        var q = HttpUtility.ParseQueryString(stateString);
        q.Add(ctx.Request.QueryString);
        q.Remove("state");

        ctx.RewritePath(ctx.Request.Path + "?" + q);
    }
}

Step 2. Add one reference to System.Web.Extensions

Step 3. In the FacebookProviderAuthorizer.cs (Nopcommerce project) look for the FacebookClient Property private FacebookClient _facebookApplication;

This should refer to your new file just added.

Step 4. Now put a break point in the method named VerifyAuthentication in the file FacebookProviderAuthorizer.cs .

The authResult.IsSuccessful must be true now as it successfully parsed the token.

Thanks all. Please like if the soluutions worked for you.