Add user login, signup, and session.

app/Admin/Login/page.tsx

@@ -1,7 +1,24 @@
-import UnderConstruction from "@/components/static_pages/UnderConstruction";
+import { useState } from "react";
 
+import { login, signup } from "@/lib/server_functions/userAuth";
 export default function Login() {
+  const [createAccount, setCreateAccount] = useState(false);
+
   return (
-    <UnderConstruction />
-  )
-}
+    <div>
+      <form action={createAccount ? login : signup}>
+        <input type="text" name="username" placeholder="Username" required />
+        <input
+          type="password"
+          name="password"
+          placeholder="Password"
+          required
+        />
+        <button type="submit">{createAccount ? "Login" : "Signup"}</button>
+      </form>
+      <button onClick={() => setCreateAccount(!createAccount)}>
+        {createAccount ? "Don't have an account?" : "Already have an account?"}
+      </button>
+    </div>
+  );
+}