zkFetch.js

_fetch, but with a zkproof_

Overview

This library lets you fetch any remote resource over an https endpoint. Along with the response, you also get a proof of correct execution of the fetch that can be verified by a third party.

For example, if you do a fetch with a private api key that the third party doesn't have access to, how do you prove to them that you executed the fetch correctly using the api key, and not sharing with them an arbitrary or tampered response? zkfetch.

Key features:
- Generate verifiable proofs of HTTP requests
- Support for private credentials (API keys, auth headers) and secret params
- Response matching and redaction
- Built on Reclaim Protocol

Installation

``bash


Install the package

npm install @reclaimprotocol/zk-fetch

Download required ZK proof files

node node_modules/@reclaimprotocol/zk-fetch/scripts/download-files
`

Prerequisites

- Node.js version 18 or higher
- An application ID and secret from the Reclaim Developer Portal

Quick Start

`javascript
const { ReclaimClient } = require("@reclaimprotocol/zk-fetch");

// Initialize client
const client = new ReclaimClient('APPLICATION_ID', 'APPLICATION_SECRET');

// Make a verified request
const proof = await client.zkFetch('https://api.coingecko.com/api/v3/simple/price?ids=ethereum&vs_currencies=usd', {
method: 'GET',
headers: {
accept: 'application/json'
}
}, {
responseMatches: [{
type: 'regex',
value: 'ethereum":{"usd":(?.*?)}}',
}],
responseRedactions: [{ regex: 'ethereum":{"usd":(?.*?)}}'}],
});
`




Authentication Methods

zkFetch supports two authentication modes depending on where you're running the code:

$3

Use this when running on a secure server (Node.js backend). Your application secret stays safe on the server.

`javascript
const { ReclaimClient } = require('@reclaimprotocol/zk-fetch');

// Backend only - never expose secret in frontend!
const client = new ReclaimClient('APPLICATION_ID', 'APPLICATION_SECRET');

const proof = await client.zkFetch('https://api.example.com/data', {
method: 'GET'
});
`

$3

Use this for browsers or untrusted environments. Your application secret never leaves your backend.

Step 1: Generate signature on your backend

`javascript
const { generateSessionSignature } = require('@reclaimprotocol/zk-fetch');

// Backend API endpoint
app.post('/api/get-signature', async (req, res) => {
const signature = await generateSessionSignature({
applicationId: process.env.APP_ID,
applicationSecret: process.env.APP_SECRET,
allowedUrls: [
'https://api.coingecko.com/*', // Wildcard - all paths under domain
'https://api.example.com/public/data', // Exact URL match
'^https://api\\.example\\.com/user/\\d+$' // Regex pattern
],
expiresAt: Math.floor(Date.now() / 1000) + 3600 // Expires in 1 hour (optional)
});

res.json({ signature });
});
`

Step 2: Use signature in your frontend

`javascript
const { ReclaimClient } = require('@reclaimprotocol/zk-fetch');

// Fetch signature from your backend
const response = await fetch('/api/get-signature');
const { signature } = await response.json();

// Initialize with signature - safe for frontend!
const client = new ReclaimClient(
'APPLICATION_ID',
signature
);

// Make requests (only to URLs in allowlist)
const proof = await client.zkFetch(
'https://api.coingecko.com/api/v3/simple/price?ids=bitcoin&vs_currencies=usd',
{ method: 'GET' }
);
`

Signature Features:
- Time-limited (default 1 hour, max 72 hours)
- URL-restricted via allowlist (exact, wildcard, or regex patterns)
- Cryptographically signed (ECDSA)
- No secrets exposed to frontend

URL Pattern Examples:
- 'https://api.example.com/data' - Exact match only
- 'https://api.example.com/*' - All paths under domain
- '^https://api\\.example\\.com/user/\\d+$' - Regex pattern for dynamic URLs




Client Configuration

You can enable logging by passing true as the argument:

`javascript
const client = new ReclaimClient('APPLICATION_ID', 'APPLICATION_SECRET', true); // logs enabled
`

$3

TEE (Trusted Execution Environment) mode can be enabled per-request by setting useTee: true in the options:

`javascript
const proof = await client.zkFetch('https://api.example.com/data', {
method: 'GET',
useTee: true // Enable TEE mode for this specific request
});
`




Usage

$3

If the endpoint you want to _fetch_ and generate a proof of the response. This endpoint is public, and doesn't need any private data like auth headers/api keys.

This is useful when
- Verifier needs to verify without re-doing the api call
- The API doesn't need any private headers or auth
- The proof or response needs to be generated for a particular endpoint now, and verified later

`
const publicOptions = {
method: 'GET', // or POST or PUT
headers : {
accept: 'application/json, text/plain, /'
}
}
const proof = await client.zkFetch(
'https://your.url.org',
publicOptions
)
`

Note : all the data in the publicOptions will be visible to them who you share the proof with (aka, verifier).

$3

If you want to _fetch_ and generate a proof of the response, but the fetch involves some private data like auth headers or api keys

This is useful when
- Using API keys
- Using Auth headers

`
const publicOptions = {
method: 'GET', // or POST
headers : {
accept: 'application/json, text/plain, /'
}
}

const privateOptions = {
headers {
apiKey: "123...456",
someOtherHeader: "someOtherValue",
}
}

const proof = await client.zkFetch(
'https://your.url.org',
publicOptions,
privateOptions
)

`

All the data in the privateOptions will stay hidden to the verifier.

$3

You can add secret params to the request. This won't be revealed in the proof and hidden from the verifier.

For example, here's how you can make a POST request with a body containing a JSON object that includes a secret value
`
const publicOptions = {
method: 'POST',
body: JSON.stringify({
'param1': '{{value}}'
})
}

const privateOptions = {
paramValues: {
'value': 'secret_value'
}
}

const proof = await client.zkFetch(
'https://your.url.org',
publicOptions,
privateOptions
)
`

This will replace the '{{value}}' in the body with 'secret_value' and send the request to the server. but the secret_value will remain hidden from the verifier and will not be revealed in the proof.

$3

You can add cookieStr to the request. This won't be revealed in the proof and hidden from the verifier.

`
const privateOptions = {
cookieStr: 'cookie_value'
}
`




$3

You can also use responseMatches and responseRedactions to match and redact the response. This is useful when you want to verify the response against a particular value or redact some part of the response.

`
const publicOptions = {
method: 'GET', // or POST
headers : {
accept: 'application/json, text/plain, /'
}
}

const privateOptions = {
responseMatches: [
{
type: 'contains' | 'regex', // type of match
value: '' | '', // value to match or regex to match
}
],
responseRedactions: [
{
jsonPath: '$.data', // JSON path to redact
xPath: '/data', // Xpath to redact
regex: '', // Regex to redact
}
]
}

const proof = await client.zkFetch(
'https://your.url.org',
publicOptions,
privateOptions
)
`

$3

You can add context to your proof request, which can be useful for providing additional information:

`
const publicOptions = {
context: {
contextAddress: '0x0000000000000000000000000000000000000000',
contextMessage: 'message'
}
}
`




Using the response

The response looks like the follows
`
{
claimData: {
provider: 'http',
parameters: '{"body":"","method":"GET","responseMatches":[{"type":"regex","value":"ethereum\\":{\\"usd\\":(?.*?)}}"}],"responseRedactions":[],"url":"https://api.coingecko.com/api/v3/simple/price?ids=ethereum&vs_currencies=usd"}',
owner: '0x96faf173bb7171a530b3e44f35f32d1307bda4fa',
timestampS: 1725377559,
context: '{"contextAddress":"0x0000000000000000000000000000000000000000","contextMessage":"message","extractedParameters":{"price":"2446.75"},"providerHash":"0xe5a9592ed030d011f1755f392c07aea1f3cb0492ad8910254b25f80ad556e3bb"}',
identifier: '0x8518b246857a47658edc8314319305c1fb5eb666ec3ee36ae07e1564c73ff288',
epoch: 1
},
identifier: '0x8518b246857a47658edc8314319305c1fb5eb666ec3ee36ae07e1564c73ff288',
signatures: [
'0x02d14b5f3377875ecab84125e53c2387b7b1a50b4762840b33dd24117326b88670818e24668aa65c5e80f8d71c192ba5803a9ca1415d72a81f3efcf1341379d41c'
],
extractedParameterValues: { price: '2446.75' },
witnesses: [
{
id: '0x307832343438393735373233363865616466363562666263356165633938643865353434336139303732',
url: 'wss://witness.reclaimprotocol.org/ws'
}
]
}
`

$3

#### Verify the proofs

Install @reclaimprotocol/js-sdk

`bash
$ npm install @reclaimprotocol/js-sdk
`

Import the verifyProof function from the js-sdk

`javascript
const { verifyProof } = require('@reclaimprotocol/js-sdk');
`

Use verifyProof(proof)

You must send the proofObject and not the verifiedResponse to the verifier for them to be able to verify.

`javascript
const isProofVerified = await verifyProof(proof);
`

it verifies the authenticity and completeness of a given proof. It checks if the proof contains signatures, recalculates the proof identifier, and verifies it against the provided signatures. If the verification fails, it will log the error and return false.

#### Transform proof for onchain

Transforms proof data into a format suitable for on-chain transactions, you need to use it before sending the proof to the blockchain.

Import the transformForOnchain function from the js-sdk

`javascript
const { transformForOnchain } = require('@reclaimprotocol/js-sdk');
`

Use transformForOnchain(proof) to transform the proof for onchain.

`javascript
const onchainProof = transformForOnchain(proof);
`




$3

You can add retries and timeout to the fetch request. The default value for retries is 1 and timeout is 1000ms.

`
const publicOptions = {
method: 'GET', // or POST
headers : {
accept: 'application/json, text/plain, /'
}
}

const privateOptions = {
headers {
apiKey: "123...456",
someOtherHeader: "someOtherValue",
}
}

const proof = await client.zkFetch(
'https://your.url.org',
publicOptions,
privateOptions,
5, // retries
10000 // retryInterval
)
`

$3

You can add geolocation information to your fetch request. The default value for geoLocation is null.

Note: The geoLocation should be a two-letter ISO country code, for example, 'US' for the United States.

`
const publicOptions = {
method: 'GET', // or POST
headers : {
accept: 'application/json, text/plain, /'
}
// geoLocation should be a two-letter ISO country code, e.g., 'US' for the United States
geoLocation: 'US'
}

const proof = await client.zkFetch(
'https://your.url.org',
publicOptions,
)

``

More examples

you can find more examples/starter packs here

- React Example
- Express Example
- NestJS Example
- Next.js Example

License

This library is governed by an AGPL license.
That means, you can fork, modify and use for commercial use as long as the entire project is fully open sourced under an AGPL License.

If you wish to use commercially use this library in a closed source product, you must take permission.