def sign(self, message):
		"""
		>>> authlen = OmapiHMACMD5Authenticator.authlen
		>>> len(OmapiHMACMD5Authenticator(b"foo", 16*b"x").sign(b"baz")) == authlen
		True

		@type message: bytes
		@rtype: bytes
		@returns: a signature of length self.authlen
		"""
		return hmac.HMAC(self.key, message, digestmod=hashlib.md5).digest()