Move back cookie fetch to SignInForm. Role fetched and saved into a Context. Small refactorings.

src/api/PrivateRoute/PrivateRoute.tsx

-import React, { useState, useEffect } from 'react';
+import React, { useState, useEffect, useContext } from 'react';
 import axios from 'axios';
 import { Route, Redirect, RouteProps } from 'react-router-dom';
 import { NonAuthRoutes } from 'api/routes';
+import { AuthContext } from 'components/AuthUser/AuthContext';
+import { Roles } from 'api/userRoles';
 
 /**
  * A wrapper for <Route> that redirects to the login screen if you're not yet authenticated.
+ * Every non-public route must be wrapped with this component.
  * */
 
 type Props = {
@@ -20,27 +23,28 @@ export const PrivateRoute = ({
   requiredRoles,
 }: Props): JSX.Element => {
   const [auth, setAuth] = useState<boolean>(false);
-  const [loading, setLoading] = useState<boolean>(false);
+  const { role } = useContext(AuthContext);
 
   useEffect(() => {
     const fetch = async (): Promise<unknown> => {
       const result = await axios('/api/web/login/is_authenticated');
       setAuth(result.data.is_authenticated);
-      setLoading(true);
       return null;
     };
-    fetch();
-  }, []);
-
-  const currentRole = String(sessionStorage.getItem('ROLE'));
-  const userHasRequiredRole = requiredRoles.includes(currentRole);
+    /*
+    Check if user is logged in.
+    Avoiding this condition would call is\_authenticated every time
+    this component state is triggered, falling in unnecessary calls to the
+    server.
+    */
+    if (role !== Roles.visitor) fetch();
+  }, [auth]);
+  const userHasRequiredRole = requiredRoles.includes(role);
   const message = userHasRequiredRole
     ? 'Please log in to view this page'
     : 'Your role is not allowed';
 
-  return !loading ? (
-    <p>loading</p>
-  ) : (
+  return (
     <Route
       exact={false}
       path={path}
@@ -51,7 +55,7 @@ export const PrivateRoute = ({
           <Redirect
             to={{
               pathname: userHasRequiredRole
-                ? NonAuthRoutes.signIn
+                ? `${NonAuthRoutes.auth}${NonAuthRoutes.signIn}`
                 : NonAuthRoutes.unauthorized,
               state: {
                 message,