Secure Proxed.AI Calls in Expo / React Native Using Apple DeviceCheck

TL;DR – You'll build a custom Expo dev client, fetch a DeviceCheck token on iOS, then send Authorization: Bearer <partialKey>.<token> to Proxed.AI. That's it.

Why Do I Need This?

• Protect the real provider key. Proxed uses a split-key model. Your app only knows the client part (partialKey) – the server part lives safely on Proxed. • Block emulators, scripts & jail-broken devices. DeviceCheck proves the request came from a legitimate iOS installation of your app. • Keep development friction-free. Test Mode + a test key lets you skip DeviceCheck when you're iterating.

How Authentication Works with Proxed

The first segment of the Bearer token is always treated as the partial key, so you never have to send x-ai-key when using the recommended flow.

1 – Prerequisites

1. Apple Developer account.
2. DeviceCheck enabled for your App ID + a DeviceCheck private key (.p8), Key ID and Team ID (see Apple DeviceCheck guide).
3. A Proxed project with: • Device Check configured (upload that .p8). • A partial API key (OpenAI, Anthropic, etc.).
4. Expo SDK ✹ 49+ and EAS CLI installed.

2 – Install Packages

npx expo install react-native-device-info
# optional, but handy for custom config plugins
bun add -D @expo/config-plugins

react-native-device-info already wraps the DeviceCheck native APIs.

3 – Create a Custom Dev Client

DeviceCheck isn't available in Expo Go. Generate native projects and build a dev client:

npx expo prebuild --clean          # generates ios/ & android/ directories
EAS_BUILD_PROFILE=development \
  eas build --platform ios

Install the resulting .ipa on a physical device – no simulators.

4 – Fetch the Token & Talk to Proxed

lib/proxed-service.ts:

import DeviceInfo from "react-native-device-info";
import { z } from "zod";

const ENDPOINT = "https://api.proxed.ai/v1/vision";          // or /text, /pdf, /openai/{projectId}/* ...
const PROJECT_ID = "YOUR_PROJECT_UUID";                       // path variant also works
const PARTIAL_KEY = "pk-abc123…";                             // client half of your provider key

// Define expected response structure to keep TS happy
const resultSchema = z.object({ /* … */ });
export type VisionResponse = z.infer<typeof resultSchema>;

export async function analyzeImage(base64: string): Promise<VisionResponse> {
  // 1 – Get DeviceCheck token (skip on Android / emulator)
  const isEmu = await DeviceInfo.isEmulator();
  let dcToken: string | null = null;
  if (!isEmu && DeviceInfo.getSystemName() === "iOS") {
    dcToken = await DeviceInfo.getDeviceToken(); // throws on sim
  }

  // 2 – Build headers
  const headers: Record<string, string> = {
    "Content-Type": "application/json",
    "x-project-id": PROJECT_ID,
    Authorization: `Bearer ${PARTIAL_KEY}.${dcToken ?? ""}`,
  };

  // 3 – POST to Proxed
  const res = await fetch(`${ENDPOINT}/${PROJECT_ID}`, {
    method: "POST",
    headers,
    body: JSON.stringify({ image: base64 }),
  });

  if (!res.ok) throw new Error(`Proxed error ${res.status}`);

  const json = await res.json();
  return resultSchema.parse(json);
}

Development Shortcut: Test Mode

When Test Mode is enabled in the Proxed dashboard:

headers["x-ai-key"] = PARTIAL_KEY;
headers["x-proxed-test-key"] = "YOUR_TEST_KEY"; // no Bearer needed

This bypasses DeviceCheck, letting you test on simulator / Android.

5 – Common Pitfalls

1. Expo Go? Won't work – needs custom client.
2. Simulators? generateToken() always fails. Use Test Mode or a real device.
3. Entitlements missing? Inspect the built .ipa – you need com.apple.developer.devicecheck = true.
4. Wrong Bearer format? Must be partialKey.token. No spaces, no Bearer: prefix inside the string.
5. 401 UNAUTHORIZED? Check • Project ID matches. • Partial key matches the server half. • DeviceCheck is enabled in the project. • Token is valid (base64). Use Apple's sandbox endpoint for dev keys.

6 – What Happens Server-Side?

1. Proxed splits the Bearer at the first . → partialKey, token.
2. Looks up the server part of the key.
3. Verifies the DeviceCheck token with Apple unless Test Mode is on.
4. Reassembles the full provider key in-memory only.
5. Forwards the request to OpenAI/Anthropic/etc.
6. Validates the model's response against your schema.
7. Streams / returns the validated JSON back to the app.

All within a few hundred ms.

7 – Next Steps

• Build Android variant (skip DeviceCheck but still benefits from partial keys). • Use structured responses to get type-safe JSON back. • Add consumption notifications to watch for spikes.

Happy shipping ✌️