How to get the Facebook user id using the access token

I have a Facebook desktop application and am using the Graph API. I am able to get the access token, but after that is done - I don't know how to get the user's ID.

My flow is like this:

1. I send the user to https://graph.facebook.com/oauth/authorize with all required extended permissions.

2. In my redirect page I get the code from Facebook.

3. Then I perform a HTTP request to graph.facebook.com/oauth/access_token with my API key and I get the access token in the response.

From that point on I can't get the user ID.

How can this problem be solved?

If you want to use Graph API to get current user ID then just send a request to:

https://graph.facebook.com/me?access_token=...

The easiest way is

https://graph.facebook.com/me?fields=id&access_token="xxxxx"

then you will get json response which contains only userid.

The facebook acess token looks similar too "1249203702|2.h1MTNeLqcLqw__.86400.129394400-605430316|-WE1iH_CV-afTgyhDPc"

if you extract the middle part by using | to split you get

2.h1MTNeLqcLqw__.86400.129394400-605430316

then split again by -

the last part 605430316 is the user id.

Here is the C# code to extract the user id from the access token:

   public long ParseUserIdFromAccessToken(string accessToken)
   {
        Contract.Requires(!string.isNullOrEmpty(accessToken);

        /*
         * access_token:
         *   1249203702|2.h1MTNeLqcLqw__.86400.129394400-605430316|-WE1iH_CV-afTgyhDPc
         *                                               |_______|
         *                                                   |
         *                                                user id
         */

        long userId = 0;

        var accessTokenParts = accessToken.Split('|');

        if (accessTokenParts.Length == 3)
        {
            var idPart = accessTokenParts[1];
            if (!string.IsNullOrEmpty(idPart))
            {
                var index = idPart.LastIndexOf('-');
                if (index >= 0)
                {
                    string id = idPart.Substring(index + 1);
                    if (!string.IsNullOrEmpty(id))
                    {
                        return id;
                    }
                }
            }
        }

        return null;
    }

WARNING: The structure of the access token is undocumented and may not always fit the pattern above. Use it at your own risk.

Update Due to changes in Facebook. the preferred method to get userid from the encrypted access token is as follows:

try
{
    var fb = new FacebookClient(accessToken);
    var result = (IDictionary<string, object>)fb.Get("/me?fields=id");
    return (string)result["id"];
}
catch (FacebookOAuthException)
{
    return null;
}

You can use below code on onSuccess(LoginResult loginResult)

loginResult.getAccessToken().getUserId();