This should be the first plug to quickly reject requests other than POST /.

With a standard Plug.Router approach, on the other hand, requests must flow through the entire plug chain before being matched (HTTP method and path), with the result that the other plugs need to be defensive and account for invalid requests and raise the right errors. For example the JSON parser by default doen’t try to parse bodies of GET requests (because they don’t have a body), which means that the conn.assigns.events property doesn’t get populated.

Responds with 404 for non / requests and with 405 for non POST requests. Lets legit requests pass through.