Best practices

We recommend storing the tokens in your backend as part of the user account. Ideally, these tokens shouldn't be sent to the client side again to maintain a higher level of security and lower the potential exposure of these tokens to malicious third parties through cross-site scripting (XSS) attacks.

To provide an easy way to link users with existing accounts that have opted to Sign in with Klarna you can use two properties that are returned in the id tokens, email, phone number, national identification number (in selected markets) or a combination of those. 

Each time a customer signs in with Klarna, the most recent email address and phone number will be passed to you, the merchant. This includes when the data was last verified, so if you deem the last verification too long ago, you can trigger an additional verification step. The logic for that can be based on the claims email_verified and phone_verified.

When a customer signs in with Klarna, it's likely that they will also wish to pay with Klarna. Therefore, we recommend that you configure Klarna to be preselected in the checkout. To simplify the checkout even further, you can present only Klarna as a payment option.

Boost conversion by pre-filling shoppers’ personal details when they check out. You can do this by leveraging data already obtained during the Sign in with Klarna session. This way, returning users simply need to confirm their information instead of entering it manually. We've found this typically results in a 5x faster checkout compared with standard checkout experiences, as well as a 10% uplift in Klarna conversion rate.

Klarna data shows that over 75% of orders have matching shipping and billing information, therefore, use these details to prefill both the shipping and billing details in your checkout.

Shoppers who need to change this information, however, should still be able to click Change and enter a separate shipping address or method, if needed.