Communication with a web page via the user's SAPGUI takes place for SAP ERP via the SAP OCI (Open Catalog Interface). The parameters for the web page to be called are maintained in a so-called call hierarchy (such as user, password, the URL of the page). Part of this is a worthless parameter HOOK_URL. This parameter can then be used on the website as the return address (Action URL for POST). The SAPGUI then dynamically enters the URL of the SAP ERP with a reference to the user's SAP process.
<form name="hookForm" action="SAPEVENT:POST" method="post"> <input type="hidden" name="HOOK_URL" value = "SAPEVENT:POST">