Create a Google auth server

[j-rewerts]

We currently don't authenticate against our own server to provide Google Sign In. This is an insecure design and can be improved. There are 2 main tasks:

• Use the LiveChat Visitor SDK on the server to impersonate our users
• Use Google Sign In to authenticate our users.

Note that this issue doesn't track work related to actually using this backend.

[j-rewerts]

After investigating the first issue, it appears LiveChat's Visitors SDK depends on many features from the browser. It references both the global document and the window object. It would be possible to mock out much of this interaction, but that would be pretty sketchy.

LiveChat support told me they're working on a Customer API that will allow us to get much of this functionality built in.