In fact the problem was a typo:
if (is_a($auth, 'iAUTH_plugin') && ($plugin->lookupUser(array('username' => $username, 'password' => $password)))) {
instead of
if (is_a($plugin, 'iAUTH_plugin') && ($plugin->lookupUser(array('username' => $username, 'password' => $password)))) {
In fact the problem was a typo: >lookupUser( array(' username' => $username, 'password' => $password)))) { >lookupUser( array(' username' => $username, 'password' => $password)))) {
if (is_a($auth, 'iAUTH_plugin') && ($plugin-
instead of
if (is_a($plugin, 'iAUTH_plugin') && ($plugin-
Fixed at rev 910.