APIKeyMiddlewareGenerator creates a middleware to fetch an API key from a header and store it in a context key.

AuthenticationMiddlewareGenerator generates auth middleware that looks up a session ID, and attaches a Session to the request context (at `sesskey`).

AuthUser uses the passed-in auth methods to authenticate the user.

ExposeResponseWriterMiddleware configures an http.Handler (like any Connect server) to place the responseWriter in its context.

GetAPIKey works with APIKeyMiddlewareGenerator to return an API key in the passed-in context.

InternalErr sends a 500, it is a good way of transparently passing through an error.