Hash-based Message Authentication Code Tool

It would be awesome if there was a tool to encrypt and decrypt data with HMAC like what is done in C# here http://msdn.microsoft.com/en-us/library/system.security.cryptography.hmacsha512(v=vs.110).aspx

I would like this because certain RESTful web services I need to consume in Warewolf require their payload to be signed this way and currently is not possible without writing a custom plugin. Which I then need to manage on the file system of my server... Not keen to go this route.