Can Atmosphere be used for persistent connection from behind the firewall?

[Afgan47]

I have a requirement to connect to my cloud service from , on premise service which is residing behind the firewall of computer.
Use case -> Service S1 and CS2(Cloud), S1 is reside on premise and connecting to user source, S1 will fetch data from the user source and then it will send it to cloud service CS2(S1 should open port 443 and make out bond SSL connection with CS2), now latter point of time, if any user come for authentication at CS2 service it will call S1 on premise service to authenticate with user source, Note - S1 and user source both are behind firewall.S1 can open port 443 and make out bond SSL connection with CS2 >this is one way, how can I can connect on demand from CS2 to S1(behind the firewall)
How can I use Atmosphere in this case? Kindly suggest and also share some sample code