Handling anonymous users in community

I am new and have searched for an answer but cannot find a complete match.

What I want to achieve is that anonymous users are cannot create accounts in community, but they can read everything posted.

We have an alternate workflow where users are created on Zendesk via Hubspot, and we want this to be the only method for creating community members. Basically, I do not want members of the public having the ability to create an account and post. We have to create the account only via our internal process.

Any help of pointers would be appreciated!