Cloud Manager allows you to work with a proxy server.
You can set it up during the Setup stage (In the Setup Wizard) or at a later time - Just click the top right menu (Small triangle),
go to "Settings" and enter the URL to the proxy.
I am happy to share that in Cloud Manager 3.0 (Released on June 30th) we are now supporting proxy servers with Basic Authentication as well.
In the same "Settings" menu you can enter the username/password in case it is needed.
Hope that helps!
Cloud Solution Architect