be able to specify more specific routing for the upstream server

[cdepillabout]

Currently, goat-guardian works like the following:

If a request comes in on the path /twitter/login or /twitter/callback, goat-guardian handles it directly. If a request comes in on any other path (like /some/other/page.html), goat-guardian forwards the request to the upstream server.

It would be nice to be able to specify "routing rules" for goat-guardian.

For instance, if a request comes in on a path like /static/img/*, then forward it to static-img-server.example.com. If a request comes in on any other path, then forward it to app-server.example.com.

In order to be able to specify something like this, we probably need to write these routing rules in a configuration file. That means that #17 needs to be implemented before we can do this issue.

We are imagining that these routing rules would be able to be specified like they are in Webpack:

https://webpack.js.org/configuration/dev-server/#devserver-proxy