problem explanation

README.md

@@ -33,3 +33,81 @@ mvn compile exec:java
 http://localhost:8000/
 
 Login with user/password: demo-user/demo-user
+
+
+# Problem I'm trying to solve
+
+This is a single page application using axios to call the Vert.x API backend.
+
+It is working like the vanilla Vert.x Oauth2 example: 
+https://github.com/vert-x3/vertx-examples/tree/b6194db5b5e7eac3173f8c968c9ecac8e4a567f9/web-examples/src/main/java/io/vertx/example/web/oauth2
+
+Except that HTML is not produced by the backend (with templates) but by Vue.js and it is calling the backend with axios.
+
+The app has 2 "pages":
+- `/#`  
+- `/account`
+
+The `/account` "page" is calling the API to get user data
+
+```javascript
+    async mounted() {
+       try {
+           const response = await api.get("/api/account")
+           this.token = response.data.token
+           this.email = response.data.email
+       } catch (error) {
+            this.error = "an error occurred while fetching your account from the server: " + error
+       } finally {
+            this.loading = false
+       }
+    }
+
+```
+
+The app is globally configured to go to the /# page in case of HTTP 401 error:
+```javascript
+const vm = new Vue ({
+    router,
+    el: "#app",
+    beforeMount() {
+        const self = this;
+        api.interceptors.response.use(function (response) {
+            return response;
+          }, function (error) {
+            if (error.response && error.response.status === 401)
+                self.$router.push({path: "/signin"});
+            return Promise.reject(error);
+          }
+        );
+    }
+}).$mount("#app");
+```
+
+When no route is specified, the app will try to show the `/account` page:
+```javascript
+const routes = [
+    { path: "/", redirect: { path: "/account" } },
+    { path: "/signin", component: Signin },
+    { path: "/account", component: Account }
+];
+```
+
+So the idea is:
+
+1. you're landing on /
+2. the vue router redirects you to the /account page
+3. an API call is performed
+4. you receive a 401 error
+5. you're redirected to the /signin page
+
+Problem is if you don't have this Vert.x modification:
+https://github.com/bfreuden/vertx-vue-oauth2-example/commit/796c92fa18aa2162299d30bd6f0287e030d98b52
+
+Then axios is not receiving a 401 error, it is receiving a generic `AxiosError: Network Error` because of the redirect.
+
+So you can't distinguish between "I'm not authenticated" and "the server down". 
+This seems to be by browser design and there is nothing you can do.
+
+
+