This can already be done within the confines of the phpbb tools. We can make a new subforum where people require authorization to post but not to read. If there is a forum game that needs this then submit a request to the mod team, but as it stands now community/moderator enforcement of verbal requests to have people outside the game not post seems effective enough.

Does this need to be enforced by the forum software, though?

In the past, we've run SoW threads where only certain players were permitted to post, and it worked well with only community enforcement.

I don't think phpBB has this feature.

Ah, yes. That would be good. An example for not-game-threads: Mods are discussing about updates and they want that other people can see these but not interfere.

Now if they did this I can see it working if it was only able to be done in the forum game section of the forum; and in other sections only with mod permission.

If I create another thread like this, I won't give the password to CommanderByron.

Yeah, it would probably like this.

Let me pose the rebuttal.

What happens when someone makes a post “Liberals/Conservatives are not doing what’s best for the country.” And then only give passwords to people who agree with them. Now you have a thread with a single opinion on it and no one able to rebuttal. I’m sure the mod email will be filled with complaints.

Ah. I didn't realise that people posting in game threads was a problem.

No, everybody can read it. For example, you're playing a forum game. And you want that only registered players to post. Others won't be able to post unless they know the password.

Like a PM with several people copied in, you mean?

To talk with only specific people.

For what purpose?

Subject is enough to explain,
Would be good to creating threads with password protection, like password protected games. People can read these threads. But that will require password to write something.