C# .NET: Create AWS SDK Calls and Signing Them with .NET

The following code is using the Amazon Alexa Web Information Service to pull site information. You create the url, with query strings, and sign the request.

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string awsAccessId = "MyAccessId";
string awsSecretKey = "MySecretKey";
string alexaUrl = "http://awis.amazonaws.com/?";

Dictionary<string, string> queryStringList = new Dictionary<string, string>();    

string timeStamp = System.DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ", System.Globalization.CultureInfo.InvariantCulture);

queryStringList.Add("Url", "google.com");
queryStringList.Add("Action", "UrlInfo");
queryStringList.Add("Count", "10");
queryStringList.Add("ResponseGroup", "Rank,ContactInfo,Categories,UsageStats,Keywords,SiteData,LinksInCount");
queryStringList.Add("SignatureMethod", "HmacSHA256");
queryStringList.Add("SignatureVersion", "2");
queryStringList.Add("Start", "1");
queryStringList.Add("Timestamp", timeStamp);

//sort
queryStringList = queryStringList.OrderBy(x => x.Key).ToDictionary(x => x.Key, x => x.Value);

//query strings must be urlencode with special characters being in uppercase, .NET does not do this by default
//must use custom method

//access key must be first in the query string
string queryString = "";
queryString = "AWSAccessKeyId=" + UpperCaseUrlEncode(awsAccessId) + "&";

//url encode query string values
foreach (var item in queryStringList)
{
	queryString += item.Key + "=" + UpperCaseUrlEncode(item.Value) + "&";
}

//remove trailing &
queryString = queryString.TrimEnd(new char[] { '&' });

alexaUrl += queryString;

//must create signature
string stringToEncode = "GET\nawis.amazonaws.com\n/\n" + queryString;

System.Security.Cryptography.HMACSHA256 provider = new System.Security.Cryptography.HMACSHA256(System.Text.Encoding.UTF8.GetBytes(awsSecretKey));

byte[] tmpSource;
byte[] tmpHash;

//Create a byte array from source data.
tmpSource = System.Text.Encoding.UTF8.GetBytes(stringToEncode);

//Compute hash based on source data.
tmpHash = provider.ComputeHash(tmpSource);

//Convert hash to string
string endcodeQueryString = Convert.ToBase64String(tmpHash, 0, tmpHash.Length);		

alexaUrl += "&Signature=" + Server.UrlEncode(endcodeQueryString);   

...

//method to url encode a value with uppercase values for special characters
public static string UpperCaseUrlEncode(string value)
{
	char[] temp = HttpUtility.UrlEncode(value).ToCharArray();
	for (int i = 0; i < temp.Length - 2; i++)
	{
		if (temp[i] == '%')
		{
			temp[i + 1] = char.ToUpper(temp[i + 1]);
			temp[i + 2] = char.ToUpper(temp[i + 2]);
		}
	}
	return new string(temp);
}