User Session time in Phoenix

I’d like to pass user local time difference from UTC to convert displayed Phoenix data for the user.
Currently we get this minute difference with javascript below.

export var time_from_utc = {
  run: function () {
    var date = new Date()
    var minutes = date.getTimezoneOffset()
    localStorage.setItem('time_from_utc', minutes)

In Phoenix layout.html.eex

  var time_from_utc = localStorage.getItem('time_from_utc')
  if (time_from_utc) {} else { time_from_utc = 0 }
  document.cookie = 'time_from_utc = ' + time_from_utc

In Phoenix Controller


Is there any plug or better way to get/set it in user’s conn session?