aspnetmvc_discourse_sso.cs

public ActionResult DiscourseLogin()
{
    if (string.IsNullOrEmpty(Request.QueryString["sso"]) || string.IsNullOrEmpty(Request.QueryString["sig"]))
        return Content("Invalid");

    string ssoSecret = "YOUR SSO SECRET"; //must match sso_secret in discourse settings

    string sso = Request.QueryString["sso"];
    string sig = Request.QueryString["sig"];

            
    string checksum = getHash(sso, ssoSecret);
    if (checksum != sig)
        return Content("Invalid");

    byte[] ssoBytes = Convert.FromBase64String(sso);
    string decodedSso = Encoding.UTF8.GetString(ssoBytes);

    NameValueCollection nvc = HttpUtility.ParseQueryString(decodedSso);

    string nonce = nvc["nonce"];

    //TODO: Add your own get user information
    //Ensure user is logged in by adding the [Authorize]   
    //Attribute to this controller method and validate the
    //user has permission to access the forum      

    string email = "testuser@test.com";
    string username = "testuser";
    string name = "Test User";
    string externalId = "21";

    string returnPayload = "nonce=" + Server.UrlEncode(nonce) +
                            "&email=" + Server.UrlEncode(email) +
                            "&external_id=" + Server.UrlEncode(externalId) +
                            "&username=" + Server.UrlEncode(username) +
                            "&name=" + Server.UrlEncode(name);

    string encodedPayload = Convert.ToBase64String(Encoding.UTF8.GetBytes(returnPayload));
    string returnSig = getHash(encodedPayload, ssoSecret);

    string redirectUrl = ConfigurationManager.AppSettings["DiscourseUrl"] + "/session/sso_login?sso=" + encodedPayload + "&sig=" + returnSig;

    return Redirect(redirectUrl);
}

public string getHash(string payload, string ssoSecret)
{
    var encoding = new System.Text.UTF8Encoding();
    byte[] keyBytes = encoding.GetBytes(ssoSecret);
            
    System.Security.Cryptography.HMACSHA256 hasher = new System.Security.Cryptography.HMACSHA256(keyBytes);
            
    byte[] bytes = encoding.GetBytes(payload);
    byte[] hash = hasher.ComputeHash(bytes);
            
    string ret = string.Empty;
    foreach (byte x in hash)
        ret += String.Format("{0:x2}", x);
    return ret;
}