Verify signature Facebook Connect

Question

I have followed the instructions in this great Stackoverflow question but i am not sure about this verify signature thing. Is this provided in some way in the Facebook Toolkit or do i have to do something myself? The documentation is not superclear on how to do this and if it is already baked in the facebook toolkit i don't want to spend to much time on it.

Anyone have done this? Should mention i use a standard ASP.NET Web Application in C#. Any help would be appreciated!

Answer 1

At the moment, you have to do it yourself. I've provided a simple method you can call to see if the signature is valid or not.

private bool IsValidFacebookSignature()
    {
        //keys must remain in alphabetical order
        string[] keyArray = { "expires", "session_key", "ss", "user" };
        string signature = "";

        foreach (string key in keyArray)
            signature += string.Format("{0}={1}", key, GetFacebookCookie(key));

        signature += SecretKey; //your secret key issued by FB

        MD5 md5 = MD5.Create();
        byte[] hash = md5.ComputeHash(Encoding.UTF8.GetBytes(signature.Trim()));

        StringBuilder sb = new StringBuilder();
        foreach (byte hashByte in hash)
            sb.Append(hashByte.ToString("x2", CultureInfo.InvariantCulture));

        return (GetFacebookCookie("") == sb.ToString());
    }

    private string GetFacebookCookie(string cookieName)
    {
        //APIKey issued by FB
        string fullCookie = string.IsNullOrEmpty(cookieName) ? ApiKey : ApiKey + "_" + cookieName;

        return Request.Cookies[fullCookie].Value;
    }

Note: SecretKey and ApiKey are values provided by Facebook that you need to set.

Answer 2

You can do this using FBConnectAuth, it does the same as above, and a little more.