WordPress fix for "Missing Author" and "Missing Updated Date" Google structured data errors.

missingAuthorUpdatedFix.css

.hatom-extra {
  font-style: italic;
  margin-top: 10px;
  padding-top: 10px;
  font-size: 12px;
}

missingAuthorUpdatedFix.php

<?php

// 
// By Zeshan Ahmed
// URI: http://www.zeshanahmed.com/
// 

/* Fix "Missing Author" and "Missing Updated" issue - START */
add_filter( 'the_content', 'custom_author_code');

function custom_author_code($content) {
  if (is_singular() || is_single()) {
    return $content . '<div class="hatom-extra"><span class="title">'. get_the_title() .'</span> was last modified: <span class="updated"> '. get_the_modified_time('F jS, Y') .'</span> by <span class="author vcard"><span class="fn">'. get_the_author() .'</span></span></div>' ;
  } else {
    return $content;
  }
}
/* Fix "Missing Author" and "Missing Updated" issue - END */