fix: Add callback debugging

pkg/spamasaurusrex/main.go

@@ -36,6 +36,7 @@ func callbackHandler(w http.ResponseWriter, r *http.Request) {
 	code := r.URL.Query().Get("code")
 	token, err := config.Exchange(r.Context(), code)
 	if err != nil {
+		w.Write([]byte(spew.Sdump(err)))
 		http.Error(w, "Error exchanging code for token", http.StatusInternalServerError)
 		return
 	}