Fix Insecure API Management in SvelteKit

SvelteKit's convenience is a double-edged sword. Insecure API management usually manifests as leaking sensitive keys via '$env/static/public' or exposing internal logic directly to the client. If your API keys are visible in the browser's Network tab, you've already lost. Real security requires enforcing a strict server-side boundary using private environment variables and proxy routes.

The Vulnerable Pattern

// src/routes/search/+page.svelte
, {
headers: { ‘X-API-KEY’: PUBLIC_INTERNAL_API_KEY }
});
return await response.json();
}

The Secure Implementation

The fix implements the Proxy Pattern. By moving the fetch logic to a '+server.js' file, we use '$env/static/private' which SvelteKit guarantees will never be bundled into client-side code. This prevents credential leakage. We also leverage the 'locals' object (populated by hooks) to perform server-side authorization checks before the upstream request is even made, mitigating unauthorized access to sensitive internal endpoints.

// src/routes/api/proxy/+server.js
import { INTERNAL_API_KEY } from '$env/static/private';
import { json, error } from '@sveltejs/kit';
export async function GET({ url, locals }) {
// 1. Authorization: Ensure the user is authenticated
if (!locals.user) throw error(401, ‘Unauthorized’);
const query = url.searchParams.get(‘q’);
// 2. Server-side Fetch: The secret key never leaves the server
const response = await fetch(https://api.backend.internal/v1/search?q=${query}, {
headers: { ‘X-API-KEY’: INTERNAL_API_KEY }
});
if (!response.ok) throw error(response.status, ‘Upstream Error’);
const data = await response.json();
return json(data);
}