Fix Insecure API Management in Blitz.js

Blitz.js abstracts the API layer through its Zero-API RPC approach, but this abstraction often leads to a false sense of security. Attackers can hit RPC endpoints directly, bypassing UI-level guards. Insecure API Management in Blitz usually manifests as Broken Object Level Authorization (BOLA) or missing authentication middleware. To secure it, you must enforce server-side validation using resolver pipes and session context.

The Vulnerable Pattern

import { resolver } from "@blitzjs/rpc";
import db from "db";
// VULNERABLE: This mutation accepts any ID and data without verifying session or ownership.
export default resolver.pipe(async ({ id, …data }) => {
const user = await db.user.update({ where: { id }, data });
return user;
});

The Secure Implementation

The secure implementation utilizes three layers of defense. First, 'resolver.zod' enforces strict input validation, preventing injection and mass assignment. Second, 'resolver.authorize()' acts as a functional gatekeeper, rejecting unauthenticated requests. Third, and most importantly, we implement an explicit ownership check using 'ctx.session.userId'. By comparing the session context against the requested resource ID, we mitigate BOLA attacks where an authenticated user attempts to modify another user's data.

import { resolver } from "@blitzjs/rpc";
import db from "db";
import * as z from "zod";
const UpdateUserSchema = z.object({ id: z.number(), name: z.string().optional() });
export default resolver.pipe(
resolver.zod(UpdateUserSchema),
resolver.authorize(), // 1. Ensure the user is authenticated
async ({ id, …data }, ctx) => {
// 2. BOLA Check: Verify the session user owns the resource or is an admin
if (ctx.session.userId !== id && ctx.session.role !== “ADMIN”) {
throw new Error(“Unauthorized: You do not own this resource.”);
}
const user = await db.user.update({
  where: { id },
  data,
  select: { id: true, name: true } // 3. Prevent sensitive data leakage
});
return user;
}
);