Hallo,
das sollte funktionieren, getestet mit TYPO 4.6 und 4.7.
 
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Hier meine ext_localconf.php:
 
t3lib_extMgm::addService($_EXTKEY,  'auth' /* sv type */,  'tx_myext_sv1' /* sv key */,
array(
	'title' => 'MyExample-Service',
	'description' => 'Authenticates against something different from TYPOs database!!!',
	'subtype' => 'authUserFE,getUserFE',
	'available' => TRUE,
	'priority' => 80,
	'quality' => 80,
	'os' => '',
	'exec' => '',
	'classFile' => t3lib_extMgm::extPath($_EXTKEY).'sv1/class.tx_myext_sv1.php',
	'className' => 'tx_myext_sv1',
));
 
-----------------
 
Die Auth-Klasse:
 
<?php
 
require_once(PATH_t3lib.'class.t3lib_svbase.php');
 
class tx_myext_sv1 extends tx_sv_authbase {
 
	var $prefixId = 'tx_myext_sv1';		// Same as class name
	var $scriptRelPath = 'sv1/class.tx_myext_sv1.php';	// Path to this script relative to the extension dir.
	var $extKey = 'myext_sv1';	// The extension key.
 
	function init()	{
		$available = parent::init();
 
		// Here you can initialize your class.
 
		// The class have to do a strict check if the service is available.
		// The needed external programs are already checked in the parent class.
 
		// If there's no reason for initialization you can remove this function.
 
		return $available;
	}
 
	function process($content='', $type='', $conf=array())	{
 
		// Depending on the service type there's not a process() function.
		// You have to implement the API of that service type.
 
		return FALSE;
	}
 
	function getUser() {
		$user = false;
 
		if ($this->login['status']=='login' && $this->login['uident'])	{			
			$GLOBALS['TSFE']->sys_page = t3lib_div::makeInstance('t3lib_pageSelect');
 
			$result = // ABFRAGE DER BENUTZER AUF DEINER TABELLE ($this->login['uname'], $this->login['uident'])
			if($result->count() > 0) { // Benutzer gefunden 				
				$user = $this->fetchUserRecord('mydummyuser1'); // LADE DUMMY BENUTZER DIESER MUSS EXISTIEREN
				$user['username'] = $this->login['uname']; // MAPPE DIE GELADENEN DATEN DES DUMMY BENUTZERS
         		        $user['password'] = $this->login['uident'];
			}
		}	
		return $user;
	}
 
	function authUser($user) {
 
		// return values:
		// 200 - authenticated and no more checking needed - useful for IP checking without password
		// 100 - Just go on. User is not authenticated but there's still no reason to stop.
		// false - this service was the right one to authenticate the user but it failed
		// true - this service was able to authenticate the user	
		$OK = 200;
		if ($this->login['uident'] && $this->login['uname'] && $user != false)	{
			$OK = $this->compareUident($user, $this->login); // true if login-data matched
		}
 
		return $OK;
	}
}
 
 
 
if (defined('TYPO3_MODE') && $TYPO3_CONF_VARS[TYPO3_MODE]['XCLASS']['ext/myext_auth/sv1/class.tx_myextauth_sv1.php'])	{
	include_once($TYPO3_CONF_VARS[TYPO3_MODE]['XCLASS']['ext/myext_auth/sv1/class.tx_myextauth_sv1.php']);
}
 
?>
 
--------------------
 
Wichtig der DUMMY-USER muss natürlich in der Tabelle fe_users mit passender PID angelegt sein. 
Die Auth-Klasse liegt unter typo3conf\ext\myext\sv1\class.tx_myext_sv1.php
Typo3 - Cache löschen nicht vergessen.
 
Viel Erfolg!

$TYPO3_CONF_VARS['FE']['loginSecurityLevel']  = 'normal';