authenticate: refactor middleware, logging, and tests (#30)

- Abstract remaining middleware from authenticate into internal.
- Use middleware chaining in authenticate.
- Standardize naming of Request and ResponseWriter to match std lib.
- Add healthcheck / ping as a middleware.
- Internalized wraped_writer package adapted from goji/middleware.
- Fixed indirection issue with reverse proxy map.

authenticate/handlers_test.go

@@ -77,7 +77,7 @@ func TestAuthenticate_SignInPage(t *testing.T) {
 	if status := rr.Code; status != http.StatusOK {
 		t.Errorf("handler returned wrong status code: got %v want %v", status, http.StatusOK)
 	}
-	body := []byte(rr.Body.String())
+	body := rr.Body.Bytes()
 
 	tests := []struct {
 		name  string