Polished auth flow including ReservedRoute and role selection.

src/api/getRoles.ts

+import axios from 'axios';
+
+/**
+ * Ask the server all the roles of an user if the user has multiple roles.
+ * @returns array of roles.
+ */
+export const getRoles = async (): Promise<string[]> =>
+  axios('/api/web/login/get_roles').then((res) => res.data.roles);