Function join_room_by_id_handler 

async fn join_room_by_id_handler(
    __arg0: State<ServerState>,
    __arg1: AuthenticatedClientRequest<Request>,
) -> Result<ArminiusResponse<Response>, JoinRoomByIdError>

Handler for POST /_matrix/client/v3/rooms/{roomId}/join (See https://spec.matrix.org/latest/client-server-api/#post_matrixclientv3roomsroomidjoin).

This endpoint is used to join a room by its ID.