fix usage of kundensystemId

lib/Fhp/FinTs.php

@@ -589,6 +589,8 @@ public function selectTanMode($tanMode, $tanMedium = null)
         }
         $this->selectedTanMode = $tanMode instanceof TanMode ? $tanMode->getId() : $tanMode;
         $this->selectedTanMedium = $tanMedium instanceof TanMedium ? $tanMedium->getName() : $tanMedium;
+
+        $this->kundensystemId = $this->options->kundensystemId;
     }
 
     /**

lib/Fhp/Options/FinTsOptions.php

@@ -45,6 +45,15 @@ class FinTsOptions
     /** @var int */
     public $timeoutResponse = 30;
 
+    /**
+     * The Kundensystem-Id as returned by the bank and persisted by the application code
+     * This is optional, but it prevents having to re-authenticate every time on login 
+     * if not using a persisted instance with FinTs::persist()
+     * Use DialogInitialization::getKundensystemId() on the return object of FinTs::login(), to get the current Kundensystem-Id
+     * @var string
+     */
+    public $kundensystemId;
+
     /**
      * @throws \InvalidArgumentException If the options are invalid.
      */