Simple way to add utm_medium / utm_source to any inner link inside your website, as described well here: https://support.google.com/analytics/answer/1033867?hl=en

track-click-analytics.js

jQuery(document).ready(function( $ ){

  //track single link
  var original_link1 = jQuery("a#single").attr('href');
  jQuery(elem).attr('href', original_link + '?utm_source=A&utm_medium=B&utm_campaign=C');
  
  //track multi-links
  var link_group_identifier = 'a.group';
    jQuery( link_group_identifier ).each(function(i, elem) {
      var original_link = jQuery(elem).attr('href');
      jQuery(elem).attr('href', original_link + '?utm_source=A&utm_medium=B&utm_campaign=C');
	});
  
});