verifySignature :: B.ByteString -> B.ByteString -> Request -> IO Bool
verifySignature authtoken body r = 
    case lookup "X-Twilio-Signature" $ requestHeaders r of
        Nothing                 -> return False -- If signature missing from request, must not be valid
        (Just givenSignature)   -> return $ (givenSignature ==) $ calcSignature authtoken r $ body
verifySignature :: B.ByteString -> B.ByteString -> Request -> IO Bool
verifySignature authtoken body r = 
    case lookup "X-Twilio-Signature" $ requestHeaders r of
        Nothing                 -> return False -- If signature missing from request, must not be valid
        (Just givenSignature)   -> return $ (givenSignature ==) $ calcSignature authtoken r $ body
verifySignature authtoken body r = 
    case lookup "X-Twilio-Signature" $ requestHeaders r of
        Nothing                 -> return False -- If signature missing from request, must not be valid
        (Just givenSignature)   -> return $ (givenSignature ==) $ calcSignature authtoken r $ body