User is able to specify their own hub in extension configurations.

A hub server was run locally. Its URL was used in the extension configuration. The local server was used successfully to support the extension.
To test the hub used is actually the one indicated:

Launch the chat app while the local server is not on. The chat should still launch but using the "add friend" link on another browser should not connect the two clients.
To test the default hub is used when no hub is specified, remove any input in the extension configuration screen. Launch the chat app and using another browser connect to the first client with the "Add friend" link. The clients should be able to see each other's mouse movements.