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function _calnet_add_suffix($form_id, $form_values, $form) {
  form_set_value($form['name'], $form_values['name'] .'@univ.edu');
}

/**
 * Implementation of hook_form_alter().
 */
function calnet_form_alter($form_id, &$form) {
  if (isset($form['#validate']['user_login_validate'])) {
    $form['#validate'] = array_merge(array('_calnet_add_suffix' => array()), $form['#validate']);
  }
}