function hmacSign (input, algorithm, secret) {
  return crypto.createHmac(algorithm, secret).update(input).digest('base64')
}
function hmacSign (input, algorithm, secret) {
  return crypto.createHmac(algorithm, secret).update(input).digest('base64')
}
function hmacSign ( input , algorithm , secret ) { return crypto . createHmac ( algorithm , secret ) . update ( input ) . digest ( 'base64' ) }
private utils function
 
hmac sign
@param  {String} input     hamc sign input
@param  {String} algorithm hamc sign algorithm
@param  {String} secret    hamc sign secret
@return {String}           hamc signature
private utils function hmac sign