Customizing SharePress og:meta tags with custom fields

gistfile1.txt

//Add this to your theme's functions.php file
//Modify the function to add the custom field value you are looking for

add_filter('sharepress_og_tags', 'my_sharepress_og_tags');

function my_sharepress_og_tags( $og ) {
  global $post;
  $custom_value = get_post_meta($post->ID, 'your custom field name', true);
  $og = array_merge($og, array(
    'og:title' => $og['og:title'] . " " . $custom_value
  ));
  return $og;
}