Hi Karl,
Based on what you have written, this is my understanding. You are looking to send a change to a local AD server (not Azure) and issue a change to Active Directory.
I'd recommend that you build an on-prem app (in either PHP or some other language) that can communicate with the local AD server. The page should allow for POST requests where you send information and authorization to this page that pushes the change to your local AD.
This would be a lot easier to do in AAD (entra) as you can invoke PowerShell commands to make changes, but with the on-prem solution you require an intermediary to convert those requests into local AD changes.
Perhaps this might be your answer:
https://www.manageengine.com/products/ad-manager/active-directory-api/
If this is helpful please accept answer.