I did active directory integration and created users as extension.I have 1500 users and extention,
Users will use softphone, I can easily get these users an extension secret
If you are using the Clearly Anywhere Softphone, you can easily send credentials within FreePBX by email to your users following these instructions: https://kb.clearlyip.com/FreePBX/Configuring-Clearly-Anywhere-Module.html#Sending_Users_Log_in_Emails
For bria softphone, there is an API so you can have the phone self-provision after the user gives the phone their AD credentials at startup. i.e. it then looks up the phone’s config info from a DB. Obviously you don’t want to be emailing around credentials!
So I would see what your softphone vendor supports…