Strong Customer Authentication (SCA) implementieren

Strong Customer Authentication (SCA) is a regulatory requirement designed to make online payments more secure. It requires customers to verify their identity using at least two independent authentication factors.

• Knowledge: Something only the user knows (e.g., password, PIN).
• Possession: Something only the user possesses (e.g., phone, hardware token).
• Inherence: Something the user is (e.g., fingerprint, facial recognition).

These factors must be independent, meaning compromising one doesn't compromise the others.

SCA is a key component of the Revised Payment Services Directive (PSD2), an EU regulation. PSD2 aims to enhance consumer protection, promote innovation, and improve the security of payment services across the European Economic Area (EEA).

For developers, this means ensuring your payment flows can handle dynamic authentication challenges when required, especially for transactions involving European customers and banks.

SCA is generally required for customer-initiated online payments where both the payer's bank and the payee's bank are located in the EEA. Common scenarios include:

• One-off card payments.
• First payment of a recurring series.
• Manually initiated payments (e.g., adding a new card).

It applies when a customer directly interacts with the payment process.

While broad, SCA has several exemptions to improve user experience for certain transaction types. These include:

• Low-value transactions: Payments under €30 (with limits).
• Recurring transactions: Subsequent payments in a series initiated by the merchant (after the first one is authenticated).
• Trusted beneficiaries: Customers can whitelist merchants.
• Transaction Risk Analysis (TRA): Banks may waive SCA if the transaction is deemed low-risk.

Stripe automatically evaluates transactions for these exemptions.

Stripe provides tools that automatically handle SCA requirements, making it easier for developers to comply without complex logic. Stripe's APIs are designed to dynamically trigger SCA when needed and manage the authentication flow.

This includes supporting 3D Secure 2, the primary method for card-based SCA, which offers a better user experience than its predecessor.

Stripe's Payment Intents API is central to handling SCA. A Payment Intent tracks the entire lifecycle of a payment, from creation to capture.

When a Payment Intent requires SCA, Stripe automatically:

• Determines if 3D Secure 2 is needed.
• Initiates the authentication flow (e.g., redirecting the user).
• Confirms the payment once authentication is complete.

Your application listens for status changes via webhooks.

When SCA is required, the user experience typically involves a redirection or a modal dialog:

• The customer is redirected to their bank's website or a pop-up.
• They enter a one-time password (OTP), approve via banking app, or use biometrics.
• After successful authentication, they are redirected back to your site.

This process is managed by Stripe and the card issuer, minimizing direct integration effort for you.

On your server, you'll confirm the Payment Intent after collecting payment method details from the client. Stripe handles the SCA challenge if required.

This Java snippet illustrates the server-side logic for confirming a Payment Intent. Remember, a real implementation requires a valid Stripe API key and handling client-side interactions.

It's crucial to test your SCA implementation. Stripe provides special test card numbers to simulate different SCA scenarios:

• Use card_authentication_required (e.g., 4242...4242) to force an SCA challenge.
• Use other test cards for successful payments or declines without SCA.

Always test with your application's full payment flow to ensure a smooth user experience, including redirects and webhook handling.

In this lesson, you've learned about Strong Customer Authentication (SCA), a vital security measure driven by PSD2 regulations in Europe.

• SCA requires multi-factor authentication for many online payments.
• Stripe's Payment Intents API simplifies compliance by dynamically handling authentication flows, including 3D Secure 2.
• Understanding exemptions and testing SCA flows are crucial for a robust payment integration.

Implementing SCA ensures secure and compliant transactions for your European customers.