In IIS Manager center pane, there is an icon titled "Authentication" as follows:
Clicking the icon, we get 3 items as follows:
Right clicking the Anonymous Authentication
and select edit
, we have:
Question: which one should I use? What is the difference?
"The identity of an application pool is the name of the account under which the application pool's worker process runs. By default, application pools operate under the Network Service account, which has low-level user access rights."
A specific user is a user that you can set up yourself to specify which account your server will impersonate when users access your site. I would go with IUSR and give the account the necessary privileges.
app pool id