openidonly_link_alter

gistfile1.php

<?php 

/**
 * Implementation of hook_link_alter().
 *
 * When comment links are displayed, the user/register link is displayed when
 * registrations are permitted. Here the $conf global is brought into context,
 * the setting is captured in a local variable and the loaded value in $conf
 * is changed to 0. This tricks theme('comment_post_forbidden') into displaying
 * only a login link. The original value is returned to the global $conf array.
 * The value in the database is never changed.
 */
function openidonly_link_alter(&$links, $node) {
  if (!empty($links['comment_forbidden'])) {
    global $conf;
    $user_register = variable_get('user_register', 1);
    $conf['user_register'] = 0;
    $links['comment_forbidden']['title'] = theme('comment_post_forbidden', $node);
    $conf['user_register'] = $user_register;
  }
}