Partner Secure Elements (PSE) Integration

Display sensitive card information and manage PINs securely in your client application using PSE SDK (PSE version 3 with EIP-712 two-factor authentication).

Overview

If you want to display sensitive information (such as card numbers or PINs) in your front-end, you’ll need to interact with our Partner Secure Elements (PSE) service. The easiest way to do this is by using the PSE SDK from Gnosis Pay.

To initialize the SDK, you’ll need:

• An App ID provided to you upon registration with Gnosis Pay
• An ephemeral-token retrieved from the PSE private API using mTLS authentication
• An auth module token obtained through the SIWE authentication flow
• An EIP-712 signature and nonce obtained from the challenge flow described below

PSE version 3 adds an EIP-712 wallet signature as a second factor for every sensitive operation. Pass pseVersion: 3 when constructing the SDK and include eip712Signature and eip712Nonce obtained from the challenge flow described below.

Note: pseVersion refers to the PSE SDK protocol version and is unrelated to the Gnosis Pay API path (which remains /v2).

Backend Required: mTLS authentication can only be performed from a back-end. You need a back-end responsible for retrieving the ephemeral-token and sending it to your front-end upon request. We’ll go through each step in this guide.

Once your front-end has the ephemeral-token and auth module token, it can initialize the PSE SDK and use it to display secure elements.

Here’s a diagram showing each step:

---

Secure Connection Using mTLS Authentication

Mutual TLS (mTLS) is a type of authentication in which two parties in a connection authenticate each other using the TLS protocol. Your back-end will establish an mTLS authentication with the Gnosis Pay private PSE API to receive an ephemeral-token.

How to Generate mTLS Certificates

After signing up through the Partners Dashboard, you will receive an App ID instantly, which will be used in the certificate generation below. You must first create a private key and then generate a Certificate Signing Request (CSR) using the App ID as follows:

# APP_ID is a string starting with `gp_` that you have received from Gnosis Pay
export APP_ID="gp_woop_123"

# Create a private key (NEVER share with anyone)
openssl ecparam -name prime256v1 -genkey -noout -out "${APP_ID}.key.pem"

# Create the CSR (OK to share)
openssl req -new -sha256 -key "${APP_ID}.key.pem" -out "${APP_ID}.csr.pem" -subj "/CN=${APP_ID}"

You can now share the ${APP_ID}.csr.pem file with the Gnosis Pay team. DO NOT EVER share the .key.pem file with ANYONE.

Once we receive your Certificate Signing Request, we will sign it and send you back the signed certificates. These signed certificates, along with your private key, are used to establish the connection with the PSE API.

How to Establish an mTLS Authentication (in Node.js)

You should securely store the certificates in your environment along with your private key.

Your environment should expose the certificates and private key, for example:

SIGNED_CERTIFICATES="-----BEGIN CERTIFICATE-----
ABCQz ....
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
DEFC7 ....
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
GHICc ....
-----END CERTIFICATE-----"

PRIVATE_KEY="-----BEGIN EC PRIVATE KEY-----
ABCD....
-----END EC PRIVATE KEY-----"

Here’s a Node.js implementation to request the ephemeral-token in two different ways:

Using Axios

const httpsAgent = new https.Agent({
  cert: process.env.SIGNED_CERTIFICATES,
  key: process.env.PRIVATE_KEY,
  rejectUnauthorized: true, // Ensure SSL verification
});

const ephemeralTokenRequest = await axios({
  httpsAgent: httpsAgent,
  method: "POST",
  url: `https://api-pse.gnosispay.com/api/v1/ephemeral-token`,
  headers: { "Content-Type": "application/json" },
  // Axios adds the user-agent automatically
});

import https from "https";

const httpsAgent = new https.Agent({
  cert: CERT,
  key: KEY,
  rejectUnauthorized: true,
});

const req = https.request(
  {
    hostname: "api-pse.gnosispay.com",
    path: "/api/v1/ephemeral-token",
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "User-Agent": "User-Client/1.0.0",
    },
    agent: httpsAgent,
  },
  (res) => {
    let data = "";
    res.on("data", (chunk) => {
      data += chunk;
    });

    res.on("end", () => {
      console.log("Status:", res.statusCode);

      try {
        const parsedData = JSON.parse(data);
        console.log("Response:", parsedData);
      } catch {
        console.log("Raw response:", data);
      }
    });
  }
);

req.on("error", (error) => {
  console.error("Request error:", error);
});
req.end();

The ephemeral-token, as its name suggests, is valid for a very short time frame. It is advised to generate a new one for every usage of the SDK.

---

EIP-712 Two-Factor Authentication

PSE version 3 requires a wallet signature before each sensitive operation. This acts as a second factor: even if an authModuleToken is compromised, an attacker cannot view card data or change a PIN without also controlling the user’s wallet.

How It Works

Before initializing the SDK, your front-end must:

1. Request a one-time challenge from the auth module.
2. Ask the user’s wallet to sign the returned EIP-712 typed data.
3. Pass the resulting signature and nonce to the SDK constructor.

The PSE service forwards both values to the auth module, which verifies the signature and marks the nonce as consumed. Each challenge is single-use and expires after 5 minutes.

The Challenge Endpoint

GET /pci/cards/{cardId}/challenge?action={action}
Authorization: Bearer {authModuleToken}

The action parameter determines which operation is being authorized:

action	Operation
view-details	Display card number, expiry, and security code
view-pin	Display the current PIN
change-pin	Set or change the PIN

The response is a complete EIP-712 typed data object, ready to pass directly to signTypedData:

{
  "domain": {
    "name": "Display VISA Card Details",
    "version": "1",
    "chainId": 42220
  },
  "primaryType": "Message",
  "types": {
    "Message": [
      { "name": "authorization", "type": "string" },
      { "name": "nonce", "type": "uint256" }
    ]
  },
  "message": {
    "authorization": "Display VISA Card Details",
    "nonce": "123456789012345678901234567890"
  }
}

message.nonce is returned as a decimal string representing a uint256. Convert it to BigInt before passing it to signTypedData.

Signing the Challenge

Using wagmi

import { useSignTypedData } from "wagmi";

const { signTypedDataAsync } = useSignTypedData();

// 1. Fetch the challenge (authModuleToken is sent automatically via client config)
const { data, error } = await getPciCardsByCardIdChallenge({
  path: { cardId },
  query: { action: "view-details" },
});

if (error || !data) throw new Error("Failed to get EIP-712 challenge");

// 2. Sign — convert nonce to BigInt for the uint256 type
const signature = await signTypedDataAsync({
  domain: data.domain,
  types: data.types,
  primaryType: data.primaryType,
  message: {
    authorization: data.message.authorization,
    nonce: BigInt(data.message.nonce),
  },
});

// 3. Pass to SDK constructor
const eip712Signature = signature;
const eip712Nonce = data.message.nonce; // keep as decimal string

import { createWalletClient, custom } from "viem";
import { celo } from "viem/chains";

const walletClient = createWalletClient({
  chain: celo,
  transport: custom(window.ethereum),
});

// 1. Fetch the challenge
const response = await fetch(
  `/pci/cards/${cardId}/challenge?action=view-details`,
  { headers: { Authorization: `Bearer ${authModuleToken}` } }
);
const data = await response.json();

// 2. Sign
const [account] = await walletClient.getAddresses();
const signature = await walletClient.signTypedData({
  account,
  domain: data.domain,
  types: data.types,
  primaryType: data.primaryType,
  message: {
    authorization: data.message.authorization,
    nonce: BigInt(data.message.nonce),
  },
});

const eip712Signature = signature;
const eip712Nonce = data.message.nonce;

The challenge must be fetched immediately before each SDK initialization. Do not reuse a nonce across different operations or SDK instances — it will be rejected after the first use.

---

How to Use the PSE SDK

Installation

npm install @gnosispay/pse-sdk

Backend: Ephemeral Token Relay

Your backend needs an endpoint that proxies ephemeral token requests to the PSE private API using mTLS. Here’s an example using Express:

import express from "express";
import axios from "axios";
import https from "node:https";

const app = express();

app.get("/api/ephemeral-token", async (_req, res) => {
  try {
    const cert = Buffer.from(process.env.CLIENT_CERT, "base64").toString("ascii");
    const key = Buffer.from(process.env.CLIENT_KEY, "base64").toString("ascii");
    const httpsAgent = new https.Agent({ cert, key, rejectUnauthorized: true });

    const response = await axios({
      method: "POST",
      url: "https://api-pse.gnosispay.com/api/v1/ephemeral-token",
      headers: { "Content-Type": "application/json" },
      httpsAgent,
    });

    res.json({ data: response.data.data });
  } catch (error) {
    res.status(502).json({ error: "Failed to reach PSE private API" });
  }
});

In this example, CLIENT_CERT and CLIENT_KEY are the base64-encoded signed certificate and private key stored in your environment variables.

Frontend: Initialize the SDK

After completing the EIP-712 challenge/sign step above, initialize the SDK with pseVersion: 3:

import GPSDK, { ElementType } from "@gnosispay/pse-sdk";

// 1. Get the auth module access token from your SIWE auth flow
const authModuleToken = getAccessToken(); // your auth implementation

// 2. Fetch ephemeral token from your backend
const response = await fetch("/api/ephemeral-token");
const { data } = await response.json();

// 3. Fetch and sign an EIP-712 challenge (see section above)
//    Use the action matching the operation you are about to perform:
//    "view-details" | "view-pin" | "change-pin"
const { eip712Signature, eip712Nonce } = await getSignedChallenge(cardId, "view-details");

// 4. Initialize the SDK with PSE version 3
const gpSdk = new GPSDK({
  pseVersion: 3,                          // PSE version 3 — required for EIP-712 2FA
  appId: "gp_your_app_id",               // Your Partner App ID
  ephemeralToken: data.ephemeralToken,
  authModuleToken: authModuleToken,       // Auth module access token
  eip712Signature: eip712Signature,       // Hex signature from wallet
  eip712Nonce: eip712Nonce,               // Decimal nonce string from challenge
  onActionSuccess: (action) => {
    console.log("Action completed:", action);
  },
  onInvalidToken: (message) => {
    console.error("Token invalid:", message);
    // Refresh the ephemeral token and reinitialize
  },
  onError: (message, details) => {
    console.error("PSE error:", message, details);
  },
});

The authModuleToken expires every 15 minutes. Handle the onInvalidToken callback to refresh your access token via the token refresh flow and re-initialize the SDK.

Display Card Details

Use ElementType.CardData to display the full card number, expiration date, and security code.

Use action: "view-details" when fetching the EIP-712 challenge for this element.

// cardId is a UUID obtained from GET /cards
const { destroy } = gpSdk.init(ElementType.CardData, "#card-data-container", {
  cardId: "019c9578-a8ce-7445-9961-51b945605f70",
});

// Call destroy() when unmounting or cleaning up
destroy();

View Card PIN

Use ElementType.CardPin to display the card’s current PIN inside the secure iframe.

Use action: "view-pin" when fetching the EIP-712 challenge for this element.

// Fetch and sign the challenge with action "view-pin" before constructing the SDK
const { eip712Signature, eip712Nonce } = await getSignedChallenge(cardId, "view-pin");

const gpSdk = new GPSDK({
  pseVersion: 3,
  appId: "gp_your_app_id",
  ephemeralToken: data.ephemeralToken,
  authModuleToken: authModuleToken,
  eip712Signature,
  eip712Nonce,
  onActionSuccess: (action) => { /* ... */ },
  onInvalidToken: (message) => { /* ... */ },
  onError: (message, details) => { /* ... */ },
});

const { destroy } = gpSdk.init(ElementType.CardPin, "#pin-container", {
  cardId: "019c9578-a8ce-7445-9961-51b945605f70",
});

Set / Change Card PIN

Use ElementType.SetCardPin to render a PIN entry form that lets the cardholder set or change their PIN.

Use action: "change-pin" when fetching the EIP-712 challenge for this element.

// Fetch and sign the challenge with action "change-pin" before constructing the SDK
const { eip712Signature, eip712Nonce } = await getSignedChallenge(cardId, "change-pin");

const gpSdk = new GPSDK({
  pseVersion: 3,
  appId: "gp_your_app_id",
  ephemeralToken: data.ephemeralToken,
  authModuleToken: authModuleToken,
  eip712Signature,
  eip712Nonce,
  onActionSuccess: (action) => {
    // Fired with Action.SetPin when the user submits the new PIN,
    // and Action.DoneSettingPin when the operation is confirmed.
    console.log("PIN operation completed:", action);
  },
  onInvalidToken: (message) => { /* ... */ },
  onError: (message, details) => { /* ... */ },
});

const { destroy } = gpSdk.init(ElementType.SetCardPin, "#set-pin-container", {
  cardId: "019c9578-a8ce-7445-9961-51b945605f70",
});

Refresh Ephemeral Token

If you need to refresh the ephemeral token without re-creating the SDK instance:

const newToken = await fetchNewEphemeralToken();
gpSdk.refreshToken(newToken);

Callbacks

The SDK provides three callbacks to handle events from the iframe:

Callback	Trigger
onActionSuccess(action)	A user action completes (e.g., CardNumberCopied, SetPin, DoneSettingPin)
onInvalidToken(message)	The ephemeral token has expired or is invalid
onError(message, details)	An error occurred inside the iframe

---

How to Customize the Style of Secure Elements in the iframe

For security reasons, the only way to apply custom styling to iframe elements is to prepare and share a CSS file with the Gnosis Pay team. This file, named <partner_name>.css, will be incorporated into the iframe.

Standard styling is applied to the iframe elements by default. You can override the style of these classes and IDs as needed. Here are some of them:

Card Data

• .pse-container - A shared class for all iframe containers.
• #pse-card-data-container - The main container for displaying card data.
• .pse-card-field - The container for each card data field (card number, expiry date, security code).
• .pse-card-label - Labels for each field.
• .pse-card-value - The container for the actual card data values.

---

Styling Guide

Here is a suggested workflow to customize the styling:

1. In your front-end, load the element you wish to customize (e.g., the card data).
2. Locate the custom CSS file with your name in either the “Style Editor” in Firefox or the “Sources” panel on Chrome/Brave. In the example below, the file is gnosis_pay_ui.css.
3. Apply your desired styling. The changes will be reflected in your interface immediately.
4. Save the file and send it to Gnosis Pay for application in production.

Here is an example of overriding the .pse-card-field class in Firefox: