I ran your app and I got this warning:
bundle.js:sourcemap:8738 Warning: Cannot update a component (SessionContextProvider) while rendering a different component (App). To locate the bad setState() call inside App, follow the stack trace as described in https://reactjs.org/link/setstate-in-render at App (http://localhost:3001/static/js/bundle.js:141:125) at SessionContextProvider (http://localhost:3001/static/js/bundle.js:641:90) at Router (http://localhost:3001/static/js/bundle.js:36104:15) at BrowserRouter (http://localhost:3001/static/js/bundle.js:35584:5)

Despite the fact that everything works well in this example, to my mind it is not the best solution becouse when you visit public page and then you want to log in, there is no redirect to last visited page. Imagine that you are reading article and with no reason you want to log into your account( or for example, you want to add comment), after you logged you should be redirect to this article in case to not looking for this article again. I hope you will head this problem.
Thanks for your work, your code helped me a lot.