Hi Denny Regehr thank you for your comment and the idea. Just to be sure I understand it correctly. Do you mean a note field where the TEXT of the certificate is stored? Or do you mean a certificate field as an attachment?

Regarding the expiration date and notification: A TimerJob or something similar is needed for this request. The next problem is: all data is encrypted and can be decrypted ONLY with the master password. This means: the expiration date cannot be read if it is not decrypted and this is only possible with the master password. And I/the timer job do not know the master password. That means you would have to implement the same encryption and decryption logic in the timerjob (The timerjob would have to know the page URL, webpart instance ID and the masterpassword (not hashed)). In addition, there are fees for the TimerJob. I think it would be easier in this case to just take a list, (possibly only for a certain group of people) and build a flow that determines the date from the items and notifies you. The certificate itself doesn't even have to be stored in the list, it could still be in the WebPart :-)