implement a simple request token session garbage collector

lib/util.php

@@ -358,12 +358,30 @@ class OC_Util {
 	 * Todo: Write howto
 	 */
 	public static function callRegister(){
+		//mamimum time before token exires
+		$maxtime=(60*60);  // 1 hour
+
 		// generate a random token.
 		$token=mt_rand(1000,9000).mt_rand(1000,9000).mt_rand(1000,9000);
 
 		// store the token together with a timestamp in the session.
 		$_SESSION['requesttoken-'.$token]=time();
 
+		// cleanup old tokens garbage collector
+		// only run every 20th time so we dont waste cpu cycles
+		if(rand(0,20)==0) {  
+			foreach($_SESSION as $key=>$value) {
+				// search all tokens in the session
+				if(substr($key,0,12)=='requesttoken') {
+					if($value+$maxtime<time()){
+						// remove outdated tokens
+						unset($_SESSION[$key]);						
+					}
+				}	
+			}
+		}
+
+
 		// return the token
 		return($token);
 	}