Who is allowed to create a user on my server?

Hi,

My name is Bob, and I'm the server of organization A. As we use the WebID-OIDC spec, a distant user logged in on her server can supposedly create an account at my place.

Under which conditions?

Does every WebID-OIDC user that is logged in somewhere on the web can create an account at my place and log into me?

Please, elaborate further.