Retrieve ALL user permissions in Site Collection

I’m looking for a PowerShell script that will search an entire site collection and return the permissions a specific user has been granted.

I’m looking for permissions either directly granted to every list, library, document, etc. OR granted via a SharePoint Group.

I found a script on TechNet which would work except running scripts in the Online environment is disabled.

I know there has to be a way because there are 3^rd party tools that you can buy that’ll do it.

Any help will be greatly appreciated!!

Regards,
Terry