How to determine a user's access to shared folders

[KenStewart]

I know which users have been granted access to a site, but I don't know how to determine all resources they have access to. I can go to any folder/file and use Manage Access=>Advanced=>Check Permissions to see if and how a particular user can access the entity, but that's time consuming for a large tree and many users.

I don't necessarily want to deny any access at this point, but I'd like to see where we may need to reconsider permissions  granted in the past that are no longer appropriate. We generally use groups to manage permissions, but sometimes there are exceptions . . . .

[#2 · Accepted solution]

Not a built in way provided by SPO so the options here are:
(1) Create your permission reports writing PS code / Grabbing existing code
(2) Use third party tools that provide this kind of reports such as SysKit Security Manager or Sharegate

[#3]

Thanks, @Juan Carlos González Martín. Good advice. I looked at the SysKit and Sharegate software, both interesting but pricey for a very small company like ours. I wasn't looking at such a complete solution, but there may be real value there.

On the PS code, I could take a stab but that's a stretch for my current skills. Can you suggest any good repositories with SP code?