code: function (input, signature, b64safeKey, alg) {
    var key = new Buffer( b64url.b64( b64safeKey ), 'base64' )
    var hmac = crypto.createHmac( alg, key ).update( input )
    var inputSignature = b64url.safe( hmac.digest( 'base64' ) )
    return (inputSignature === signature)
  }
docs: ******************************************************************
  verify and sign code