I'm not sure if that's correct. This is my hmac function: https://gist.github.com/anonymous/23f2597b19da01f36297

And, for example, this is what it returns: Br7UX6pke+gzxmEP8HUFXzNuIqPJlU+qfqMZiXeJ7N3oZ+fynQZ3g1D12nxNHFZDo0KWZZZ+Qxy4K7+OlUHBFw==

I don't think I need to change it into hexadecimal, I tried using your function and I get the same error.