Add the ability to multiplex multiple ApplicationSessions over a single transport

First of all, thank you for creating autobahn-python (and Crossbar). Autobahn-python is a great library and has been very helpful to our company. As we've been using autobahn-python, we've been investigating how to set ourselves up to be able to scale with increased usage. We believe we have some good options with being able to increase servers that should take care of most problems. Additionally, we want to make sure that we are able to fully utilize any servers that we are running.

We currently have the following setup:

• Devices open a connection to a python web server.
• The web server then uses autobahn-python to create a connection to Crossbar for each device that connects to the web server (using autobahn.asyncio.wamp.ApplicationSession and autobahn.asyncio.websocket.WampWebSocketClientFactory).

Given this model, we expect the number of connections from each python web server to Crossbar to grow to the tens of thousands. Since these are all essentially connections that come from the same place and go to the same place, it feels excessive to need tens of thousands of open TCP connections to maintain the ApplicationSessions.

Thus, this issue is a request to consider adding support for a single transport to be able to support multiple ApplicationSessions.

Digging through the autobahn-python codebase, it looked like the ApplicationSession was pretty well isolated from the underlying transport. It also felt like it is possible to write a version of a transport that manages allowing multiple ApplicationSessions to join the transport.

Are there plans to add support for allowing multiple sessions over a single transport? Are there any issues or design decisions that would prohibit this request?

Start by reading autobahn.asyncio.wamp.ApplicationSession and autobahn.asyncio.websocket.WampWebSocketClientFactory to trace how sessions currently connect to and use a transport. Define the session multiplexing and lifecycle behavior before identifying changes; done means multiple ApplicationSessions can share one transport instead of opening separate TCP connections.