> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/tokenization/implement-tokenization/post-tokenization-requests/update-the-digital-card-assurance-method-e-commerce-only/device-binding-flow.md).

# Token binding

Typically, a token requestor, such as a merchant, starts a token binding request because the end user is ready to pay with a token. Token binding restricts token use and increases confidence in its legitimacy.

D1 receives the request and orchestrates the workflow using the registered data. The issuer backend does not require new APIs. The level of issuer backend involvement depends on the integration model selected by the issuer.

Because token binding involves a device, the issuer can define untrusted device types during D1 onboarding. D1 uses this data to decline a binding request when the TSP provides the required device information.

The following table lists the information that the issuer can use to define untrusted devices:

| Rule name                        | Description                                                                                      |
| -------------------------------- | ------------------------------------------------------------------------------------------------ |
| Device types not trusted         | The issuer can select device types that it does not trust. For example, devices of type `WATCH`. |
| Device manufacturer              | The issuer can list device manufacturers that it does not trust.                                 |
| Device manufacturer - OS version | If known, the issuer can specify an OS version that it does not trust.                           |
| Device manufacturer - FW version | If known, the issuer can specify a firmware version that it does not trust.                      |

Without rules for untrusted devices, D1 always requires **step-up authentication** for each binding request.

### Sequence diagrams

The following sequence diagrams show the full flow orchestrated by D1 and the level of involvement of the issuer backend.

<figure><img src="https://2043231064-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FW6dljaTEEzefPQILRFB7%2Fuploads%2FPKFjXkkxTM703j5MdeH8%2Fimage.png?alt=media&amp;token=8b378b34-75cf-471f-94f1-91105b268473" alt=""><figcaption></figcaption></figure>

<figure><img src="https://2043231064-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FW6dljaTEEzefPQILRFB7%2Fuploads%2FFU1aa303qlrDhgsC8tby%2Fimage.png?alt=media&amp;token=409428ab-c688-40a2-b246-d1252ecd9c78" alt=""><figcaption></figcaption></figure>

If no untrusted devices have been defined, or if no device matches the defined rules, D1 always performs **step-up authentication** and provides the list of available ID\&V methods.

For ID\&V prerequisites, see [Prerequisites for ID\&V methods](/tokenization/implement-tokenization/post-tokenization-requests/update-the-digital-card-assurance-method-e-commerce-only.md#prerequisites-for-id-and-v-methods).

#### OTP verification by SMS or email

The following sequence diagram shows the flow when the end user chooses OTP by SMS or email for verification:

<figure><img src="https://2043231064-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FW6dljaTEEzefPQILRFB7%2Fuploads%2FMbMWSw3y6RfljwhHmfyV%2FSequence%20Diagram%20-%20OTP%20verification%20by%20SMS%20or%20email.png?alt=media&amp;token=5bfc4ac1-3c89-4537-a02b-8d66b4dbecb2" alt=""><figcaption></figcaption></figure>

The `Deliver step-up method` in step `08` still corresponds to the [Deliver OTP](/tokenization/integrate-the-d1-api/d1-api-reference/outbound-api-from-d1/consumer-api.md#post-banking-d1-v1-issuers-issuerid-consumers-consumerid-otp) API. This API delivers the selected ID\&V method, which is an OTP in this case.

If the issuer backend manages OTP delivery, it must implement [Deliver OTP](/tokenization/integrate-the-d1-api/d1-api-reference/outbound-api-from-d1/consumer-api.md#post-banking-d1-v1-issuers-issuerid-consumers-consumerid-otp) API  and use the `otp.reason` field to distinguish this request from a Tokenization request. It can use `deliveryChannel` to determine the message type:

* `otp.reason` = `DEVICE-BINDING`
* `deliveryChannel` = `SMS` or `EMAIL`

#### Verification by the issuer application

The following sequence diagram shows the flow when the end user chooses the issuer application as the verification method:<br>

<figure><img src="https://2043231064-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FW6dljaTEEzefPQILRFB7%2Fuploads%2FUZxPvli60oRSzkwbsL2O%2Fimage.png?alt=media&amp;token=29ef0c12-3ec1-47da-b710-6a9338ad6e10" alt=""><figcaption></figcaption></figure>

As described in the [High-level flow](/tokenization/implement-tokenization/post-tokenization-requests/update-the-digital-card-assurance-method-e-commerce-only.md#high-level-flow) section, the issuer backend must handle the integration required in step `[02]`. The shared data depends on the TSP. Compared with a Tokenization flow, use the following mapping to populate `StepupAuthenticationResult` correctly:

<table><thead><tr><th width="228.45458984375">D1</th><th width="261.727294921875">Mastercard</th><th>Visa</th></tr></thead><tbody><tr><td><code>authenticationId</code></td><td><code>authenticationCorrelationId</code></td><td><code>lifeCycleTraceID</code></td></tr></tbody></table>

#### Verification by issuer application using an issuer-managed trigger

The issuer can support verification in the issuer application using a PUSH message. This avoids relying on the merchant application to trigger the issuer application.

{% hint style="warning" %}
This option is supported only under these conditions:

* The issuer supports Mastercard cards. Only Mastercard can propagate this type of ID\&V option to the merchant.
* The issuer does not rely on the D1 OBO service to send messages to the end user. In that case, Thales cannot send the PUSH message on behalf of the issuer.
  {% endhint %}

The following diagram shows this flow:

<figure><img src="https://2043231064-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FW6dljaTEEzefPQILRFB7%2Fuploads%2Fo6Q0gRWxxCXM5Awa8Hpg%2FSequence%20Diagram%20-%20Verification%20by%20Issuer%20App%20with%20issuer-managed%20trigger.svg?alt=media&amp;token=e72948b6-59ea-46ea-9ad6-10bedd36b186" alt=""><figcaption></figcaption></figure>

The `Deliver step-up method` in step `04` still corresponds to the [Deliver OTP](/tokenization/integrate-the-d1-api/d1-api-reference/outbound-api-from-d1/consumer-api.md#post-banking-d1-v1-issuers-issuerid-consumers-consumerid-otp) API. This API delivers the selected ID\&V method, in this case a PUSH message. To identify this case, the issuer must check the following fields:

* `otp.reason` = `DEVICE-BINDING`
* `deliveryChannel` = `PUSH`
* `deviceInformation.deviceReference`
* `digitalCardId`

To report the result through `StepupAuthenticationResult`, the issuer must send the following value along with `digitalCardId`:

* `authenticationId` = `deviceInformation.deviceReference`

{% hint style="warning" %}
In this case, no `otp.value` is provided.

The issuer is free to manage the PUSH message content and format.
{% endhint %}


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