C#.NET Transfer Script.

This is a complete transfer script written in C#. I've been working on this the past couple days, and now that it's finished, I'd like to help others avoid some of the difficulties I've had.

I'd like to note that MUCH of this code (mostly the hard parts) is based on the examples found in this thread: http://discussions.apple.com/thread.jspa?messageID=2710342&#2710342. I've tried to credit the orignal poster in my comments.

protected void Page_Load(object sender, EventArgs e)
{
// Define your site's information. Replace these
// values with ones appropriate for your site.
string debugSuffix = "/your debug suffix";
string sharedSecret = "YOUR SHARED SECRET";
string credential1 = "your credential@urn:mace:itunesu.com:sites:school.edu";
string siteUrl = "https://deimos.apple.com/WebObjects/Core.woa/Browse/school.edu";


// Define the user information. Replace the credentials with the
// credentials you want to grant to that user, and the optional
// identity information with the identity of the current user.
// For initial testing and site setup, use the singe administrator
// credential defined when your iTunes U site was created. Once
// you have access to your iTunes U site, you will be able to define
// additional credentials and the iTunes U access they provide.
string[] credentialArray = {};
string displayName = "Demo";
string emailAddress = "demo@school.edu";
string userName = "demo";
string userIdentifier = "0";

// Append your site's debug suffix to the destination if you
// want to receive an HTML page providing information about
// the transmission of credentials and identity between this
// program and iTunes U. Remove this code after initial
// testing to instead receive the destination page requested.
// uncomment the line below to access debug information from the
// iTunes U server.
//siteUrl = siteUrl + debugSuffix;

//We create the token pieces...
string identity = getIdentityString(displayName, emailAddress, userName, userIdentifier);
string credentials = getCredentialsString(credentialArray);
string currentTime = getCurrentTime();

//...then encode and concatenate them...
string token = "credentials=" + Uri.EscapeDataString(credentials) + "&identity=" + Uri.EscapeDataString(identity) + "&time=" + currentTime;

//...and then perform three replaces because Uri.EscapeDataString doesn't properly encode spaces, "(", or ")"
token = token.Replace("%20", "+");
token = token.Replace("(", "%28");
token = token.Replace(")", "%29");

//Generate the signature string
string signature = "&signature=" + GenerateSignature(token, sharedSecret);

//Pass the token, signature, and url to the actual page request
requestSite(token + signature, siteUrl);
}

//This method creates the time needed for the signature it is based on code originally posted by "Ed at NAIT"
private string getCurrentTime()
{
DateTime epoch = new DateTime(1970, 1, 1, 0, 0, 0, 0);
TimeSpan span = DateTime.UtcNow - epoch;
int elapsed = (int)span.TotalSeconds;

return elapsed.ToString();
}

//Concatenate the identity string from the defined user information
private string getIdentityString(string displayName, string emailAddress, string userName, string userIdentifier)
{
string identity = "\"" + displayName + "\" " + "<"(" + userName + ") " + "[" + userIdentifier + "]";
return identity;
}

// concatenates all the passed in credentials into a string
// with a semicolon delimiting the credentials in the string.
private string getCredentialsString(Array credentialArray)
{
string credential = "";
int credentialCount = credentialArray.Length;

for (int i = 0; i < credentialCount; i++)
{
if (i == 0)
{
credential = credentialArray.GetValue(i).ToString();
}
else
{
credential += ";" + credentialArray.GetValue(i).ToString();
}
}
return credential;
}

//This method creates hex encoded signature. It is code originally posted by "Ed at NAIT"
public string GenerateSignature(string token, string sharedSecret)
{
//get the bytes of shared key
byte[] key = System.Text.Encoding.ASCII.GetBytes(sharedSecret);

//Get the HMACSHA256 Object for the shared key
System.Security.Cryptography.HMACSHA256 hmac = new System.Security.Cryptography.HMACSHA256(key);

//calculate the new key
byte[] newKey = hmac.ComputeHash(System.Text.Encoding.ASCII.GetBytes(token));

//return the hex of the new key
return ToHexString(newKey);
}

//This method converts the from ASCII to Hex. It is based on code originally posted by "Ed at NAIT"
public static string ToHexString(byte[] bytes)
{
string hexString = "";
for (int i = 0; i < bytes.Length; i++)
{
hexString += String.Format("{0:x2}", bytes.GetValue(i));
}
return hexString;
}

//This method makes the HTTP request. It is based on code originally posted by "Ed at NAIT"
public void requestSite(string signature, string siteUrl)
{
HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(siteUrl);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";

using (StreamWriter sw = new StreamWriter(req.GetRequestStream()))
{
//The token is the query string (ie. credentials=foo&identity=bar&time=111&signature=key)
sw.Write(signature);
}

using (WebResponse objResponse = req.GetResponse())
{
using (StreamReader sr = new StreamReader(objResponse.GetResponseStream()))
{
//This will write the html to launch iTunes if succsessful or the error if unsuccessful
Response.Write(sr.ReadToEnd());
}
}

}
}