This is a snippet of code I wrote while writing an API against the Mixpanel API. If you're building a raw http(s, actually -- thanks guys!) API request and you need to generate a signature for an IDictionary<string,string> of your query arguments, then this method will do it. (Simplified from a more generic implementation for readability; reimpl…

GetAuthenticationUriSubstring.cs

using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace Mixpanel.Security {
	public class MixpanelApiAuthenticator {
		private const string MIXPANEL_API_SECRET = @"Here's your secret, son";

		public string GetAuthenticationUriSubstring(IDictionary<string, string> queryArguments) {
			return queryArguments
				.Keys
				.OrderBy(s => s)
				.Aggregate(string.Empty,
					(accum, s) => accum += string.Format("{0}={1}", s, queryArguments[s]),
					s => {
						var accumPlusApiSecret = string.Format("{0}{1}", s, MIXPANEL_API_SECRET);

						var md5 = MD5.Create();
						var hash = md5.ComputeHash(Encoding.UTF8.GetBytes(accumPlusApiSecret));

						return string.Concat(
								hash.Select(b => b.ToString("X2"))
							)
							.ToLowerInvariant();
					}
				);
		}
	}
}