Strong customer authentication (SCA)

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SCA is a two-factor authentication method used to certify the origin and content of specific API requests related to sensitive operations or data (account login, transactions, card details, etc.). This is mandatory under the PSD2 regulation.

To enforce this two-factor authentication, LinkCy relies on:

• a trusted device
• either a PIN or biometrics

These requirements are achieved with a mobile SDK which has to be included in the partner's mobile app.
To use this SDK, check the SDK Library page.
This SDK is provided by Wultra, a trusted and secured solution for 2-Factor Authentication

This SDK will ensure that the device is trusted and will also handle the PIN or biometrics authentication.

Once the SDK is implemented, trusted device has to be declared for each enduser : see Device registration.

Then, each "SCA eligible" API endpoint will require a specific flow, to ensure that SCA is performed and validated : see Operation Data Signing.

Device registration

To onboard a device, use the "Register a device" endpoint.

You will have to provide:

The endpoint will return :

{
"activationQrCodeData": "string",
"activationCode": "string",
"activationCodeSignature": "string",
"scaDeviceId": "string"
}

activationCode cointains the code required by the SDK to activate the device.
activationQrCodeData represent this code under QR Code format.
scaDeviceId represents the id of the device which will be registered. Registered devices will be listed in the Enduser object with their status and details.

Then follow the instructions to use this activationCode within the Mobile SDK : SCA SDK Documentation

Once activation done in the mobile SDK, you have to call the Activate a device endpoint with the previously provided scaDeviceId to finalise the registration.

If successful, user's device is registered and SCA requests can now be performed for this enduser.

Several SCA devices can be registered per enduser.
After the first registration, SCA operation is required to registered any extra device.

Device registration Sequence Diagram

Here is a generic sequence diagram for a SCA device registration. This sequence can be adapted if you use your own backend.

Direct connection to LinkCy API

Operation Data Signing

One method to authenticate SCA protected operation is Data Signing. These requests have to be done in 2 steps :

• Prepare SCA operation:

Before you can send the API request, you have to create a Signature using the Mobile SDK.
Data to be signed are : HTTP Method, URI (including path params and query params) and body (if present).
Follow the SCA SDK Documentation and provider's official instructions.

• Perform SCA operation:

Once the signature is generated, you can call the SCA Secured Endpoint in LinkCy API, using :

• DATA_SIGNING in Linkcy-SCA-Strategy
• the generated Signature in the Linkcy-SCA-Signature header

The signature will have this format :

PowerAuth pa_activation_id=\"3c193fe9-ac04-4a2e-aa85-8b3d0ed4aeab\", pa_application_key=\"EklLXwMlpZhwMLHAXyX/XWHA==\", pa_nonce=\"C2irDMhb8VR3+QBTfIsAJg==\", pa_signature_type=\"possession_knowledge\", pa_signature=\"9Z+KT9LjNEdsXYfrW2ASEy85egP2InuSGnNgsd2K2xE=\", pa_version=\"3.3\

You have to send this full Payload in the Linkcy-SCA-Signature header field.

If the signature is OK, the operation will be performed and the response will be a 200, 201 or 204 code.

Operation Signing Sequence Diagram

Here are generic sequence diagrams for a SCA-protected API request :

Direct connection to LinkCy API

Or if you have your own back-end :

Out of band authentication

SCA can also be triggered with a push notification, when the operation is not initiated from the device.
The registered device will receive a Push Notification which will trigger a SCA request.

This feature is not implemented yet, but will be available soon.

Failures

Here are the errors you can receive

If a device or a factor is not onboarded and you try an API request involving SCA, you will receive 409 - SCA_DEVICE_NOT_SET or 400 - SCA_FACTOR_NOT_SET error.

If the SCA was failed, error will be 409 - SCA_INTERACTION_DECLINED.

SCA bypass

In some specific cases, SCA can be Bypassed, using the BY_PASS option in Linkcy-SCA-Strategy.

In this case, no SCA will be required and the operation will be performed.

Check with your contacts at LinkCy to know more about this.