matrix-spec-proposals/event-schemas/schema/m.room.guest_access

{
    "type": "object",
    "title": "Controls whether guest users are allowed to join rooms.",
    "description": "This event controls whether guest users are allowed to join rooms. If this event is absent, servers should act as if it is present and has the guest_access value \"forbidden\".",
    "allOf": [{
        "$ref": "core-event-schema/state_event.json"
    }],
    "properties": {
        "content": {
            "type": "object",
            "properties": {
                "guest_access": {
                    "type": "string",
                    "description": "Whether guests can join the room.",
                    "enum": ["can_join", "forbidden"]
                }
            },
            "required": ["guest_access"]
        },
        "state_key": {
            "type": "string",
            "description": "A zero-length string.",
            "pattern": "^$"
        },
        "type": {
            "type": "string",
            "enum": ["m.room.guest_access"]
        }
    }
}