does not receive messages behind corporate proxy

[kel50]

Unfortunately the backend does not work behind a corporate proxy. The last log message is Tested current Errbot version and it is 5.2.0. Incoming messages are not recognized and logged.

[...]
2019-05-07 16:41:58,535 DEBUG    errbot.backends.CiscoWebexTeams Done! I'm connected as {botname}@webex.bot
[...]
2019-05-07 16:41:58,767 DEBUG    root                      Opening websocket connection to wss://mercury-connection-a.wbx2.com/v1/apps/wx2/registrations/{id}/messages
2019-05-07 16:41:58,973 DEBUG    urllib3.connectionpool    http://{myproxyname}:8080 "GET http://version.errbot.io/?errbot=6.0.0&python=3.7.2 HTTP/1.1" 200 5
2019-05-07 16:41:58,974 DEBUG    errbot.plugins.VersionChecker Tested current Errbot version and it is 5.2.0

When I run it without proxy, the websocket connects just fine and the bot receives messages and works as expected.

2019-05-07 16:49:40,362 DEBUG    root                      Opening websocket connection to wss://mercury-connection-a.wbx2.com/v1/apps/wx2/registrations/{id}/messages
2019-05-07 16:49:40,505 DEBUG    websockets.protocol       client - state = CONNECTING
2019-05-07 16:49:40,529 DEBUG    urllib3.connectionpool    http://version.errbot.io:80 "GET /?errbot=6.0.0&python=3.7.2 HTTP/1.1" 200 5
2019-05-07 16:49:40,530 DEBUG    errbot.plugins.VersionChecker Tested current Errbot version and it is 5.2.0
2019-05-07 16:49:40,765 DEBUG    websockets.protocol       client - event = connection_made(<asyncio.sslproto._SSLProtocolTransport object at 0x10bfd26a0>)
2019-05-07 16:49:40,893 DEBUG    websockets.protocol       client - state = OPEN
2019-05-07 16:49:40,894 INFO     root                      WebSocket Opened

Is there a way to pass a proxies parameter to the backend like the Slack backend does? I'd like to run errbot at my company and this is the only thing that keeps me from doing it.

I tested some basic stuff using the webexteamssdk module and it works just fine behind a proxy, so I think the issue is about websockets.