IT Shop - Restrict users to only one service item assignment

Hi,

In our environment we have done the following:

  • Created service items for user licenses
  • Created an IT Shop with a shelf for self service. The shelf is assigned the Self service approval policy, enabling end users to request and obtain the user licenses.

What we would like to achieve is to restrict end users to only have one assignment at a time. Meaning that if a user should not be able to request and obtain more than one license at a time, and if the user is already assigned a license, a request for a new license would either be denied or would replace the current one.

How can we achieve this? Any help is greatly appreciated.