Read OAuth2.0 Signed_Request Facebook Registration C# MVC

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北海茫月
北海茫月 2021-02-06 13:21

My question is very similar this but I guess I need to take it one step further.

Facebook says \"The data is passed to your application as a signed request. The signed_r

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  • 2021-02-06 13:41

    Based on your comment, it looks like you're still looking for the response that FB is sending. I believe it it contained in the Form collection in the HttpContext Request object. So from the page you specify as the redirect, you should be able to pull it from:

    HttpContext.Current.Request.Form("signed_request")

    Hope that helps shed some light. I'm still learning as I go so this may not be the best solution.

    thanks, Jason

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  • 2021-02-06 13:50

    Here is the code we used in the Facebook C# SDK. You don't need to do this manually if you use our sdk, but if you need to do it yourself here it is:

    /// <summary>
    /// Parses the signed request string.
    /// </summary>
    /// <param name="signedRequestValue">The encoded signed request value.</param>
    /// <returns>The valid signed request.</returns>
    internal protected FacebookSignedRequest ParseSignedRequest(string signedRequestValue)
    {
        Contract.Requires(!String.IsNullOrEmpty(signedRequestValue));
        Contract.Requires(signedRequestValue.Contains("."), Properties.Resources.InvalidSignedRequest);
    
        string[] parts = signedRequestValue.Split('.');
        var encodedValue = parts[0];
        if (String.IsNullOrEmpty(encodedValue))
        {
            throw new InvalidOperationException(Properties.Resources.InvalidSignedRequest);
        }
    
        var sig = Base64UrlDecode(encodedValue);
        var payload = parts[1];
    
        using (var cryto = new System.Security.Cryptography.HMACSHA256(Encoding.UTF8.GetBytes(this.AppSecret)))
        {
            var hash = Convert.ToBase64String(cryto.ComputeHash(Encoding.UTF8.GetBytes(payload)));
            var hashDecoded = Base64UrlDecode(hash);
            if (hashDecoded != sig)
            {
                return null;
            }
        }
    
        var payloadJson = Encoding.UTF8.GetString(Convert.FromBase64String(Base64UrlDecode(payload)));
        var data = (IDictionary<string, object>)JsonSerializer.DeserializeObject(payloadJson);
        var signedRequest = new FacebookSignedRequest();
        foreach (var keyValue in data)
        {
            signedRequest.Dictionary.Add(keyValue.Key, keyValue.Value.ToString());
        }
    
        return signedRequest;
    }
    
    /// <summary>
    /// Converts the base 64 url encoded string to standard base 64 encoding.
    /// </summary>
    /// <param name="encodedValue">The encoded value.</param>
    /// <returns>The base 64 string.</returns>
    private static string Base64UrlDecode(string encodedValue)
    {
        Contract.Requires(!String.IsNullOrEmpty(encodedValue));
    
        encodedValue = encodedValue.Replace('+', '-').Replace('/', '_').Trim();
        int pad = encodedValue.Length % 4;
        if (pad > 0)
        {
            pad = 4 - pad;
        }
    
        encodedValue = encodedValue.PadRight(encodedValue.Length + pad, '=');
        return encodedValue;
    }
    

    You can find the full source code here: http://facebooksdk.codeplex.com/SourceControl/changeset/view/f8109846cba5#Source%2fFacebook%2fFacebookApp.cs

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  • 2021-02-06 13:54

    Here's how to do it using Facebook SDK

    var parsedSignedRequest = FacebookSignedRequest.Parse(FacebookApplication.Current, signed_request);
    
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