For the Spaces project there needs to be a way to allow users to join a room based on membership in a space.

An approach for this is detailed in MSC3083.

The approach will be to:

• Create an experimental room version.
• Update the auth rules based on the join_rule / experimental room version to allow users to join based on the allowed key in the m.room.join_rules event.

Note that we want this to be in an experimental room version as it is unclear whether clients will need to make changes to support this.