Linking a customer’s Klarna account to their account on your platform helps increase conversion by enabling seamless, non-interactive authentication for future payments.

Many integration strategies rely on browser-side tracking, like cookies or device-based single sign-on, to recognize returning customers. However, these methods are increasingly unreliable:

• Safari’s Intelligent Tracking Prevention (ITP) limits third-party cookies to 24 hours and deletes them after 7 days.
• Firefox Enhanced Tracking Protection blocks third-party cookies by default.
• Chrome will phase out third-party cookies entirely in 2025.
• Device fingerprints are wiped when customers clear site data, use private browsing, or update their mobile OS.

To avoid these limitations, store Klarna’s long-lived customer_token securely on your backend. This token lets you reliably recognize returning customers, regardless of browser or device, and trigger a seamless Klarna flow without requiring them to log in again.

1. Create a Klarna Payments session with intent set to buy_and_link.
   
   • For returning customers, include the previously stored customer_token in the request.
   
2. Initiate the Klarna Purchase Journey using the client_token returned in the create session response.
3. Create the order after customer confirms the purchase. Save or update the customer_token returned in the create order response. Customers can opt out from account linking, so a customer_token might not be returned in certain sessions.

First‑time customers (no token)

Send a POST request without a token to create a Klarna payments session:

Sample request - without customer_token

Returning customers (token present)

Including a valid customer_token, allows Klarna to skip the login step and load the payment form in a ready-to-buy state.

Sample request - with customer_token

curl -X POST https://api.klarna.com/payments/v1/sessions \
  -u $KLARNA_USERNAME:$KLARNA_PASSWORD \
  -H 'Content-Type: application/json' \
  -H 'Idempotency-Key: 3bcdc404-9f4c-4cd0-9d63-2d1092f361dd' \
  -d '{
        "purchase_country": "DE",
        "purchase_currency": "EUR",
        "locale": "de-DE",
        "order_amount": 25900,
        "order_tax_amount": 4130,

Once the customer confirms the purchase, create an order using the valid authorization_token.

Sample response

{
  "order_id": "12345678-1234-1234-1234-123456789abc",
  "redirect_url": "https://www.mystore.com/confirmation?order_id=12345678-1234…",
  "customer_token": "krn:partner:eu1:live:identity:customer-token:AbCdEfGh1234567"
}

Don't forget to store or update the token in your user database:

// pseudo‑code
if (order.customer_token) {
  const existing = await db.users.get(userId);
  if (existing.klarnaCustomerToken !== order.customer_token) {
    await db.users.update(userId, {
      klarnaCustomerToken: order.customer_token
    });
  }
}

Klarna may rotate tokens for security reasons. if a previously stored token is invalid or expired, Klarna will:

• Ignore the invalid token silently.
• Issue a new token in the create order response.