// token解析
var decode = function(input) {
  // Replace non-url compatible chars with base64 standard chars
  input = input
    .replace(/-/g, '+')
    .replace(/_/g, '/')

  // Pad out with standard base64 required padding characters
  var pad = input.length % 4
  if (pad) {
    if (pad === 1) {
      throw new Error('InvalidLengthError: Input base64url string is the wrong length to determine padding')
    }
    input += new Array(5 - pad).join('=')
  }

  return input
}