session context & auth util functions

client/src/context/session.ts

@@ -0,0 +1,8 @@
+import type { User } from "@chessu/types";
+
+import { createContext, Dispatch, SetStateAction } from "react";
+
+export const SessionContext = createContext<{
+    user: User | null | undefined; // undefined = hasn't been checked yet, null = no user
+    setUser: Dispatch<SetStateAction<User | null>>;
+} | null>(null);