SSO Login for Freshdesk support portal - ASP.Net C# Sample Code

sso_login_freshdesk.cs

protected void Page_Load(object sender, EventArgs e)
{
        string url = GetSsoUrl(ConfigurationManager.AppSettings["FreshDesk.BaseUrl"], //including trailing slash
                               ConfigurationManager.AppSettings["FreshDesk.Secert"], user.UserName, user.Email);
        Response.Redirect(url);
    }

string GetSsoUrl(string baseUrl, string secert, string name, string email)
{
    return String.Format("{0}login/sso/?name={1}&email={2}&hash={3}", baseUrl, Server.UrlEncode(name),
                         Server.UrlEncode(email), GetHash(secert, name, email));
}

static string GetHash(string secert, string name, string email)
{
    string input = name + email + secert;

    MD5 md5 = System.Security.Cryptography.MD5.Create();
    byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
    byte[] hash = md5.ComputeHash(inputBytes);

    StringBuilder sb = new StringBuilder();
    foreach (byte b in hash)
    {
        string hexValue = b.ToString("X").ToLower(); // Lowercase for compatibility on case-sensitive systems
        sb.Append((hexValue.Length == 1 ? "0" : "") + hexValue);
    }
    return sb.ToString();
}

I've dropped Freshdesk an email to see how we can test etc. This all seems very rushed, so my guess is they are plugging a security hole, but right now we need a test rig to know if our implementations will work once they flick the Big Red Switch!
If we have a test rig, we can just see what works. Really appreciate the comments above, hopefully one of them is the solution.

Thanks @darkpssngr, fixed.

Well, they gave us a test environment by flicking the Big Red Switch and letting us test in a live environment whilst our users couldn't login! Nice.

I'm now up and running, borrowing code from above, but very slightly different. Just in case it helps anyone, but the harder work was done by those people above, not me!

I have timestamp in the return url, not tamp.

        const string key = "XXXXXXXXXXXXXXXXXXXXXXX";
        const string pathTemplate = "https://support.XXXX.com/login/sso?name={0}&email={1}&timestamp={2}&hash={3}";
        string timems = (DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds.ToString();
        var hash = GetHash(key, alias, tbEmail.Text, timems);
        var path = String.Format(pathTemplate, Server.UrlEncode(alias), Server.UrlEncode(tbEmail.Text), timems, hash);
        Response.Redirect(path);

Same GetHash as above:
private static string GetHash(string secret, string name, string email, string timems)
{
var input = name + secret + email + timems;
var keybytes = Encoding.Default.GetBytes(secret);
var inputBytes = Encoding.Default.GetBytes(input);
var crypto = new HMACMD5(keybytes);
var hash = crypto.ComputeHash(inputBytes);
return hash.Select(b => b.ToString("x2"))
.Aggregate(new StringBuilder(),
(current, next) => current.Append(next),
current => current.ToString());
}

in python
http://www.abhiy.com/single-sign-on-remote-authentication-in-freshdesk-by-python/

I had some Encoding trouble with European Culture and Special Characters.
Here is a "Global" working version of @GrahamEHughes Code.
There are two Changes:

1. Usage of Encoding.UTF8 instead of Encoding.Default in GetHash

private static string GetHash(string secret, string name, string email, string timems)
        {
            var input = name + secret + email + timems;
            var keybytes = Encoding.UTF8.GetBytes(secret);
            var inputBytes = Encoding.UTF8.GetBytes(input);
            var crypto = new HMACMD5(keybytes);
            var hash = crypto.ComputeHash(inputBytes);
            return hash.Select(b => b.ToString("x2"))
                .Aggregate(new StringBuilder(),
                    (current, next) => current.Append(next),
                    current => current.ToString());
        }

2. Change of datetime Calculation:
   string timems = DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString();