added refreshtoken logic to backend

code/backend/src/tasks/deleteTokens.ts

@@ -0,0 +1,19 @@
+import { PrismaClient } from "../../prisma/app/generated/prisma/client";
+
+const prisma = new PrismaClient();
+
+export const deleteExpiredTokens = async () => {
+  const now = new Date();
+  try {
+    const result = await prisma.refreshToken.deleteMany({
+      where: {
+        expiresAt: {
+          lt: now, // delete expired tokens
+        },
+      },
+    });
+    console.log(`deleted ${result.count} tokens`);
+  } catch (error) {
+    console.error("Error while deleting tokens:", error);
+  }
+};