The Payment Request API provides a standard way to initiate payment requests from Web pages and applications. User agents implementing that API prompt the user to select a way to handle the payment request, after which the user agent returns a payment response to the originating site. This specification defines capabilities that enable Web applications to handle payment requests.

The Web Payments Working Group maintains a list of all bug reports that the group has not yet addressed. This draft highlights some of the pending issues that are still to be discussed in the working group. No decision has been taken on the outcome of these issues including whether they are valid. Pull requests with proposed specification text for outstanding issues are strongly encouraged.

Introduction

The Web Payments Working Group seeks to streamline payments on the Web to help reduce "shopping cart abandonment" and make it easier to deploy new payment methods on the Web. It has published the Payment Request API [[!payment-request]] as a standard way to initiate payment requests from E-Commerce Web sites and applications.

A payment app is a Web application that can handle payment requests on behalf of the user. This specification defines a number of new Web platform features to handle payment requests:

This specification does not address how software built with operating-system specific mechanisms (e.g., "native mobile apps") handle payment requests.

The term "payment app" may be useful as a shorthand for "Web app that can handle payments with Payment Request API."

This specification defines one class of products:

Conforming user agent

A user agent MUST behave as described in this specification to be considered conformant. In this specification, user agent means a Web browser or other interactive user agent as defined in [[!HTML5]].

User agents MAY implement algorithms given in this specification in any way desired, so long as the end result is indistinguishable from the result that would be obtained by the specification's algorithms.

A conforming Payment Handler API user agent MUST also be a conforming implementation of the IDL fragments of this specification, as described in the “Web IDL” specification. [[!WEBIDL-LS]]

Overview of Handling Payment Requests

In this document we envision the following flow:

  1. An origin requests permission from the user to handle payment requests for a set of supported payment methods. For example, a user visiting a retail or bank site may be prompted to register a payment handler from that origin. The origin establishes the scope of the permission but the origin's capabilities may evolve without requiring additional user consent.
  2. Payment handlers are defined in service worker code.
  3. During service worker registration, the PaymentManager is used to set:
    • A list of enabled payment methods.
    • [Optionally] the conditions under which the handler supports a given payment method; these capabilities play a role in matching computations.
    • Information used in the display of instruments supported by the payment handler.
  4. When the merchant (or other payee) calls the [[payment-request]] method show() (e.g., when the user pushes a button on a checkout page), the user agent computes a list of candidate payment handlers, comparing the payment methods accepted by the merchant with those supported by registered payment handlers. For payment methods that support additional filtering, merchant and payment handler capabilities are compared as part of determining whether there is a match.
  5. The user agent displays a set of choices to the user: the registered instruments of the candidate payment handlers. The user agent displays these choices using information (labels and icons) provided at registration or otherwise available from the Web app.
  6. When the user (the payer) selects an instrument, the user agent fires a PaymentRequestEvent (cf. the user interaction task source) in the service worker whose PaymentManager the instrument was registered with. The PaymentRequestEvent includes some information from the PaymentRequest (defined in [[!payment-request]]) as well as additional information (e.g., origin and selected instrument).
  7. Once activated, the payment handler performs whatever steps are necessary to handle the payment request, and return an appropriate payment response to the payee. If interaction with the user is necessary, the payment handler can open a window for that purpose.
  8. The user agent receives a response asynchronously once the payment handler has finished handling the request. The response becomes the PaymentResponse (of [[!payment-request]]).

An origin may implement a payment app with more than one service worker and therefore multiple payment handlers may be registered per origin. The handler that is invoked is determined by the selection made by the user of a payment instrument. The service worker which stored the payment instrument with its PaymentManager is the one that will be invoked.

Handling a Payment Request

The logic of a payment handler is driven by the payment methods that it supports. Some payment methods, such as basic-card expect little to no processing by the payment handler which simply returns payment card details in the response. It is then the job of the payee website to process the payment using the returned data as input.

In contrast, some payment methods, such as a crypto-currency payments or bank originated credit transfers, require that the payment handler initiate processing of the payment. In such cases the payment handler will return a payment reference, endpoint URL or some other data that the payee website can use to determine the outcome of the payment (as opposed to processing the payment itself).

Handling a payment request may include numerous interactions: with the user through a new window or other APIs (such as [[!WebCryptoAPI]]) or with other services and origins through web requests or other means.

This specification does not address these activities that occur between the payment handler accepting the PaymentRequestEvent and the payment handler returning a response. All of these activities which may be required to configure the payment handler and handle the payment request, are left to the implementation of the payment handler, including:

Thus, an origin will rely on many other Web technologies defined elsewhere for lifecycle management, security, user authentication, user interaction, and so on.

Structure of a Web Payment App

Architecture of a (Web) payment apps as defined in this specification.
A Web payment app is associated with an origin. Payment handlers respond to PaymentRequestEvents. PaymentManagers manage the definition, display, and user selection of PaymentInstruments. A PaymentInstrument supports one or more payment methods.

Relation to Other Types of Payment Apps

This specification does not address how third-party mobile payment apps interact (through proprietary mechanisms) with user agents, or how user agents themselves provide simple payment app functionality.

Different types of payment apps. Payment Handler API is for Web apps.
Payment Handler API enables Web apps to handle payments. Other types of payment apps may use other (proprietary) mechanisms.

Registration

Extension to the ServiceWorkerRegistration interface

This specification extends the ServiceWorkerRegistration interface with the addition of a paymentManager attribute.

        partial interface ServiceWorkerRegistration {
          readonly attribute PaymentManager paymentManager;
        };
      

PaymentManager interface

      [SecureContext, Exposed=(Window,Worker)]
      interface PaymentManager {
        [SameObject] readonly attribute PaymentInstruments instruments;
        [Exposed=Window] static Promise<PermissionState> requestPermission();
        attribute DOMString userHint;     
      };
      

The PaymentManager is used by payment apps to manage their associated instruments and supported payment methods.

instruments attribute

This attribute allows manipulation of payment instruments associated with a service worker (and therefore its payment handler). To be a candidate payment handler, a handler must have at least one registered payment instrument to present to the user. That instrument needs to match the payment methods and required capabilities specified by the payment request.

requestPermission() method

The user agent is NOT REQUIRED to prompt the user to grant permission to the origin for each new supported payment method or new payment instrument.

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. Let permission be the result of running retrieve the permission state algorithm of the permission associated with payment handler's origin.
  4. If permission is "prompt", ask the user whether allowing adding new payment instruments for the current settings object's origin is acceptable. If it is, set permission to "granted", and "denied" otherwise.
  5. Resolve p with permission.

userHint attribute

When displaying payment handler name and icon, the user agent may use this string to improve the user experience. For example, a user hint of "**** 1234" can remind the user that a particular card is available through this payment handler. When a agent displays all payment instruments available through a payment handler, it may cause confusion to display the additional hint.

PaymentInstruments interface

      [SecureContext, Exposed=(Window,Worker)]
      interface PaymentInstruments {
          Promise<boolean>           delete(DOMString instrumentKey);
          Promise<PaymentInstrument> get(DOMString instrumentKey);
          Promise<sequence<DOMString>>  keys();
          Promise<boolean>           has(DOMString instrumentKey);
          Promise<void>              set(DOMString instrumentKey, PaymentInstrument details);
          Promise<void>           clear();
      };
      

The PaymentInstruments interface represents a collection of payment instruments, each uniquely identified by an instrumentKey. The instrumentKey identifier will be passed to the payment handler to indicate the PaymentInstrument selected by the user, if any.

delete() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. If the collection contains a PaymentInstrument with a matching instrumentKey, remove it from the collection and resolve p with true.
  4. Otherwise, resolve p with false.

get() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. If the collection contains a PaymentInstrument with a matching instrumentKey, resolve p with that PaymentInstrument.
  4. Otherwise, reject p with a DOMException whose value is "NotFoundError".

keys() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. Resolve p with a Sequence that contains all the instrumentKeys for the PaymentInstruments contained in the collection, in original insertion order.

has() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. If the collection contains a PaymentInstrument with a matching instrumentKey, resolve p with true.
  4. Otherwise, resolve p with false.

set() method

When called, this method executes the following steps:

  1. Let permission be the result of running retrieving the permission state of the permission associated with payment handler's origin.
  2. If permission is not "granted", then return a Promise rejected with a NotAllowedError.
  3. If the icons member of details is present, then:
    1. Let convertedIcons be the result of running the convert image objects algorithm passing details.icons as the argument.
    2. If the convertedIcons is an empty Sequence, then return a Promise rejected with a TypeError.
    3. Set details.icons to convertedIcons.
  4. Let p be a new promise.
  5. Return p and perform the remaining steps in parallel:
  6. If the icons member of details is present, then for each icon in details.icons:
    1. If the user agent wants to display the icon, then:
      1. Let fetchedImage be the result of running the fetching image object passing icon as the argument.
      2. Set icon.[[\fetchedImage]] to fetchedImage.
  7. If the collection contains a PaymentInstrument with a matching instrumentKey, replace it with the PaymentInstrument in details.
  8. Otherwise, insert the PaymentInstrument in details as a new member of the collection and associate it with the key instrumentKey.
  9. Resolve p.

clear() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Return p and perform the remaining steps in parallel:
  3. Remove all PaymentInstruments from the collection and resolve p.

PaymentInstrument dictionary

      dictionary PaymentInstrument {
        required DOMString name;
        sequence<ImageObject> icons;
        sequence<DOMString> enabledMethods;
        object capabilities;
      };
      
name member
The name member is a string that represents the label for this PaymentInstrument as it is usually displayed to the user.
icons member
The icons member is an array of image objects that can serve as iconic representations of the payment instrument when presented to the user for selection.
enabledMethods member
The enabledMethods member is a list of one or more payment method identifiers of the payment methods supported by this instrument.
capabilities member
The capabilities member is a list of payment-method-specific capabilities that this payment handler is capable of supporting for this instrument. For example, for the basic-card payment method, this object will consist of an object with two fields: one for supportedNetworks, and another for supportedTypes.

ImageObject dictionary

      dictionary ImageObject {
          required USVString src;
          DOMString sizes;
          DOMString type;
      };
      
src member
The src member is used to specify the ImageObject's source. It is a URL from which the user agent can fetch the image’s data.
sizes member
The sizes member is used to specify the ImageObject's sizes. It follows the spec of sizes member in HTML link element, which is a string consisting of an unordered set of unique space-separated tokens which are ASCII case-insensitive that represents the dimensions of an image. Each keyword is either an ASCII case-insensitive match for the string "any", or a value that consists of two valid non-negative integers that do not have a leading U+0030 DIGIT ZERO (0) character and that are separated by a single U+0078 LATIN SMALL LETTER X or U+0058 LATIN CAPITAL LETTER X character. The keywords represent icon sizes in raw pixels (as opposed to CSS pixels). When multiple image objects are available, a user agent MAY use the value to decide which icon is most suitable for a display context (and ignore any that are inappropriate). The parsing steps for the sizes member MUST follow the parsing steps for HTML link element sizes attribute.
type member
The type member is used to specify the ImageObject's MIME type. It is a hint as to the media type of the image. The purpose of this member is to allow a user agent to ignore images of media types it does not support.

Convert image objects

When this algorithm with inputImages parameter is invoked, the user agent must run the following steps:

  1. Let outputImages be an empty Sequence of ImageObject.
  2. For each image in inputImages:
    1. If image.type is not a valid MIME type or the value of type is not a supported media format, then return an empty Sequence of ImageObject.
    2. If image.sizes is not a valid value, then return an empty Sequence of ImageObject.
    3. Let url be the result of parsing image.src with the context object's relevant settings object's API base URL.
    4. If url is failure, then return an empty Sequence of ImageObject.
    5. If url's scheme is not "https", then return an empty Sequence of ImageObject.
    6. Set image.src to url.
    7. Append image to outputImages
  3. Return outputImages.

According to the step 2.3, it is also possible to use the relative url for image.src. The following examples illustrate how relative URL resolution works in different execution contexts.

        <-- In this example, code is located in https://www.example.com/bobpay/index.html -->
        <script>

        const instrumentKey = "c8126178-3bba-4d09-8f00-0771bcfd3b11";
        const { registration } = await navigator.serviceWorker.register("/register/sw.js");
        await registration.paymentManager.paymentInstruments.set({
          instrumentKey,
          {
            name: "My Bob Pay Account: john@example.com",
            enabledMethods: ["https://bobpay.com/"],
            icons: [{
              src: "icon/lowres.webp",
              sizes: "48x48",
              type: "image/webp"
            }]
          });

        const { storedInstrument } =
          await registration.paymentManager.paymentInstruments.get(instrumentKey);

        // storedInstrument.icons[0].src == "https://www.example.com/bobpay/icon/lowres.webp";

        </script>
      

        // In this example, code is located in https://www.example.com/register/sw.js

        const instrumentKey = "c8126178-3bba-4d09-8f00-0771bcfd3b11";
        await self.registration.paymentManager.paymentInstruments.set({
          instrumentKey,
          {
            name: "My Bob Pay Account: john@example.com",
            enabledMethods: ["https://bobpay.com/"],
            icons: [{
              src: "../bobpay/icon/lowres.webp",
              sizes: "48x48",
              type: "image/webp"
            }]
          });

        const { storedInstrument } =
          await registration.paymentManager.paymentInstruments.get(instrumentKey);

        // storedInstrument.icons[0].src == "https://www.example.com/bobpay/icon/lowres.webp";
      

Registration Example

The following example shows how to register a payment handler:

        button.addEventListener("click", async() => {
          if (!window.PaymentManager) {
            return; // not supported, so bail out.
          }

          const result = await PaymentManager.requestPermission();
          if (result !== "granted") {
            return;
          }

          const { registration } =
            await navigator.serviceWorker.register('/sw.js');

          // Excellent, we got it! Let's now set up the user's cards.
          await addInstruments(registration);
        }, { once: true });

        function addInstruments(registration) {
          return Promise.all([
            registration.paymentManager.instruments.set(
              "dc2de27a-ca5e-4fbd-883e-b6ded6c69d4f",
              {
                name: "Visa ending ****4756",
                enabledMethods: ["basic-card"],
                capabilities: {
                  supportedNetworks: ['visa'],
                  supportedTypes: ['credit']
                }
              }),

            registration.paymentManager.instruments.set(
              "c8126178-3bba-4d09-8f00-0771bcfd3b11",
              {
                name: "My Bob Pay Account: john@example.com",
                enabledMethods: ["https://bobpay.com/"]
              }),

            registration.paymentManager.instruments.set(
              "new-card",
              {
                name: "Add new credit/debit card to ExampleApp",
                enabledMethods: ["basic-card"],
                capabilities: {
                  supportedNetworks:
                    ['visa','mastercard','amex','discover'],
                  supportedTypes: ['credit','debit','prepaid']
                }
              }),
            ]);
          };
     

Origin and Instrument Display for Selection

After applying the matching algorithm defined in Payment Request API, the user agent displays a list of instruments from matching payment apps for the user to make a selection. This specification includes a limited number of display requirements; most user experience details are left to implementers.

Ordering of Payment Handlers

The second bullet above may be amended to remove explicit mention of ordering defined by the payee.

The following are examples of payment handler ordering:

The Working Group has discussed two types of merchant preferences related to payment apps: (1) highlighting merchant-preferred payment apps already registered by the user and (2) recommending payment apps not yet registered by the user. The current draft of the specification does not address either point, and the Working Group is seeking feedback on the importance of these use cases. Note that for the second capability, merchants can recommend payment apps through other mechanisms such as links from their web sites.

Display of Instruments

The user agent MUST enable the user to select any displayed instrument.

The Working Group is discussing how default payment instrument display could further streamline the user experience.

Selection of Instruments

Users agents may wish to enable the user to select individual displayed Instruments. The payment handler would receive information about the selected Instrument and could take action, potentially eliminating an extra click (first open the payment app then select the Instrument).

Invocation

Once the user has selected an Instrument, the user agent fires a PaymentRequestEvent and uses the subsequent PaymentHandlerResponse to create a PaymentReponse for [[!payment-request]].

Payment Request API supports delegation of responsibility to manage an abort to a payment app. There is a proposal to add a paymentRequestAborted event to the Payment Handler interface. The event will have a respondWith method that takes a boolean parameter indicating if the paymentRequest has been successfully aborted.

Extension to ServiceWorkerGlobalScope

This specification extends the ServiceWorkerGlobalScope interface.

        partial interface ServiceWorkerGlobalScope {
          attribute EventHandler onpaymentrequest;
        };
        

onpaymentrequest attribute

The onpaymentrequest attribute is an event handler whose corresponding event handler event type is PaymentRequestEvent.

The PaymentRequestEvent

The PaymentRequestEvent represents the data and methods available to a Payment Handler after selection by the user. The user agent communicates a subset of data available from the PaymentRequest to the Payment Handler.

        [Constructor(DOMString type, PaymentRequestEventInit eventInitDict), Exposed=ServiceWorker]
        interface PaymentRequestEvent : ExtendableEvent {
          readonly attribute USVString topLevelOrigin;
          readonly attribute USVString paymentRequestOrigin;
          readonly attribute DOMString paymentRequestId;
          readonly attribute FrozenArray<PaymentMethodData> methodData;
          readonly attribute object total;
          readonly attribute FrozenArray<PaymentDetailsModifier> modifiers;
          readonly attribute DOMString instrumentKey;
          Promise<WindowClient?> openWindow(USVString url);
          void respondWith(Promise<PaymentHandlerResponse>handlerResponsePromise);
        };
      

topLevelOrigin attribute

This attribute is a string that indicates the origin of the top level payee web page. The string MUST be formatted according to the "Unicode Serialization of an Origin" algorithm defined in section 6.1 of [[!RFC6454]].

paymentRequestOrigin attribute

This attribute is a string that indicates the origin where a PaymentRequest was initialized. When a PaymentRequest is initialized in the topLevelOrigin, the attributes have the same value, otherwise the attributes have different values. For example, when a PaymentRequest is initialized within an iframe from an origin other than topLevelOrigin, the value of this attribute is the origin of the iframe. The string MUST be formatted according to the "Unicode Serialization of an Origin" algorithm defined in section 6.1 of [[!RFC6454]].

paymentRequestId attribute

When getting, the paymentRequestId attribute returns the [[\details]].id from the PaymentRequest that corresponds to this PaymentRequestEvent.

methodData attribute

This attribute contains PaymentMethodData dictionaries containing the payment method identifiers for the payment methods that the web site accepts and any associated payment method specific data. It is populated from the PaymentRequest using the MethodData Population Algorithm defined below.

total attribute

This attribute indicates the total amount being requested for payment. It is of type PaymentCurrencyAmount dictionary as defined in [[payment-request]], and initialized with a structured clone of the total field of the PaymentDetailsInit provided when the corresponding PaymentRequest object was instantiated.

modifiers attribute

This sequence of PaymentDetailsModifier dictionaries contains modifiers for particular payment method identifiers (e.g., if the payment amount or currency type varies based on a per-payment-method basis). It is populated from the PaymentRequest using the Modifiers Population Algorithm defined below.

instrumentKey attribute

This attribute indicates the PaymentInstrument selected by the user. It corresponds to the instrumentKey provided to the PaymentManager.instruments interface during registration. An empty string means that the user did not choose a specific PaymentInstrument.

openWindow() method

This method is used by the payment handler to show a window to the user. When called, it runs the open window algorithm.

respondWith() method

This method is used by the payment handler to provide a PaymentHandlerResponse when the payment successfully completes. When called, it runs the Respond to PaymentRequest Algorithm with event and handlerResponsePromise as arguments.

Should payment apps receive user data stored in the user agent upon explicit consent from the user? The payment app could request permission either at installation or when the payment app is first invoked.

PaymentRequestEventInit dictionary

            dictionary PaymentRequestEventInit : ExtendableEventInit {
              USVString topLevelOrigin;
              USVString paymentRequestOrigin;
              DOMString paymentRequestId;
              sequence<PaymentMethodData> methodData;
              PaymentCurrencyAmount total;
              sequence<PaymentDetailsModifier> modifiers;
              DOMString instrumentKey;
            };
          

The topLevelOrigin, paymentRequestOrigin, paymentRequestId, methodData, total, modifiers, and instrumentKey members share their definitions with those defined for PaymentRequestEvent

MethodData Population Algorithm

To initialize the value of the methodData, the user agent MUST perform the following steps or their equivalent:

  1. Set registeredMethods to an empty set.
  2. For each PaymentInstrument instrument in the payment handler's PaymentManager.instruments, add all entries in instrument.enabledMethods to registeredMethods.
  3. Create a new empty Sequence.
  4. Set dataList to the newly created Sequence.
  5. For each item in PaymentRequest@[[\methodData]] in the corresponding payment request, perform the following steps:
    1. Set inData to the item under consideration.
    2. Set commonMethods to the set intersection of inData.supportedMethods and registeredMethods.
    3. If commonMethods is empty, skip the remaining substeps and move on to the next item (if any).
    4. Create a new PaymentMethodData object.
    5. Set outData to the newly created PaymentMethodData.
    6. Set outData.supportedMethods to a list containing the members of commonMethods.
    7. Set outData.data to a structured clone of inData.data.
    8. Append outData to dataList.
  6. Set methodData to dataList.

Modifiers Population Algorithm

To initialize the value of the modifiers, the user agent MUST perform the following steps or their equivalent:

  1. Set registeredMethods to an empty set.
  2. For each PaymentInstrument instrument in the payment handler's PaymentManager.instruments, add all entries in instrument.enabledMethods to registeredMethods.
  3. Create a new empty Sequence.
  4. Set modifierList to the newly created Sequence.
  5. For each item in PaymentRequest@[[\paymentDetails]].modifiers in the corresponding payment request, perform the following steps:
    1. Set inModifier to the item under consideration.
    2. Set commonMethods to the set intersection of inModifier.supportedMethods and registeredMethods.
    3. If commonMethods is empty, skip the remaining substeps and move on to the next item (if any).
    4. Create a new PaymentDetailsModifier object.
    5. Set outModifier to the newly created PaymentDetailsModifier.
    6. Set outModifier.supportedMethods to a list containing the members of commonMethods.
    7. Set outModifier.total to a structured clone of inModifier.total.
    8. Append outModifier to modifierList.
  6. Set modifiers to modifierList.

Internal Slots

Instances of PaymentRequestEvent are created with the internal slots in the following table:

Internal Slot Default Value Description (non-normative)
[[\windowClient]] null The currently active WindowClient. This is set if a payment handler is currently showing a window to the user. Otherwise, it is null.
[[\fetchedImage]] undefined This value is a result of fetching image object or a fallback image provided by the user agent.
[[\respondWithCalled]] false YAHO

Handling a PaymentRequestEvent

Upon receiving a PaymentRequest by way of PaymentRequest.show() and subsequent user selection of a payment instrument, the user agent MUST run the following steps:

  1. Let registration be the ServiceWorkerRegistration corresponding to the PaymentInstrument selected by the user.
  2. If registration is not found, reject the Promise that was created by PaymentRequest.show() with a DOMException whose value is "InvalidStateError" and terminate these steps.
  3. Invoke the handle functional event algorithm with a ServiceWorkerRegistration of registration and callbackSteps set to the following steps:
    1. Set global to the global object that was provided as an argument.
    2. Create a trusted event, e, that uses the PaymentRequestEvent interface, with the event type paymentrequest, which does not bubble, cannot be canceled, and has no default action.
    3. Set the topLevelOrigin attribute of e to the origin of the top level payee web page.
    4. Set the paymentRequestOrigin attribute of e to the origin of the context where PaymentRequest was initialized.
    5. Set the paymentRequestId attribute of e to the [[\details]].id from the PaymentRequest.
    6. Set the methodData and modifiers attributes of e by executing the MethodData Population Algorithm and Modifiers Population Algorithm respectively.
    7. Set the total attribute of e to a structured clone of the total field on the PaymentDetailsInit from the corresponding PaymentRequest.
    8. Set the instrumentKey attribute of e to the instrumentKey of the selected PaymentInstrument, or the empty string if none was selected.
    9. Dispatch e to global.
    10. Wait for all of the promises in the extend lifetime promises of e to resolve.
    11. If the payment handler has not provided a PaymentHandlerResponse, reject the Promise that was created by PaymentRequest.show() with a DOMException whose value "OperationError".

Windows

An invoked payment handler may or may not need to display information about itself or request user input. Some examples of potential payment handler display include:

A payment handler that requires visual display and user interaction, may call openWindow() to display a page to the user.

Since user agents know that this method is connected to the PaymentRequestEvent, they SHOULD render the window in a way that is consistent with the flow and not confusing to the user. The resulting window client is bound to the tab/window that initiated the PaymentRequest. A single payment handler SHOULD NOT be allowed to open more than one client window using this method.

Open Window Algorithm

This algorithm resembles the Open Window Algorithm in the Service Workers specification.

Should we refer to the Service Workers specification instead of copying their steps?

  1. Let event be this PaymentRequestEvent.
  2. Let request be the PaymentRequest that triggered this PaymentRequestEvent.
  3. Let url be the result of parsing the url argument.
  4. If the url parsing throws an exception, return a Promise rejected with that exception.
  5. If url is about:blank, return a Promise rejected with a TypeError.
  6. If url's origin is not the same as the service worker's origin associated with the payment handler, return a Promise resolved with null.
  7. If this algorithm is not triggered by user activation, return a Promise rejected with a InvalidAccessError.
  8. Let promise be a new Promise.
  9. Return promise and perform the remaining steps in parallel:
  10. If event.[[\windowClient]] is not null, then:
    1. If event.[[\windowClient]].visibilityState is not "unloaded", reject promise with a DOMException whose name is "InvalidStateError" and abort these steps.
  11. Let newContext be a new top-level browsing context.
  12. Navigate newContext to url, with exceptions enabled and replacement enabled.
  13. If the navigation throws an exception, reject promise with that exception and abort these steps.
  14. If the origin of newContext is not the same as the service worker client origin associated with the payment handler, then:
    1. Resolve promise with null.
    2. Abort these steps.
  15. Let client be the result of running the create window client algorithm with newContext as the argument.
  16. Set event.[[\windowClient]] to client.
  17. Resolve promise with client.

Example of handling the PaymentRequestEvent

This example shows how to write a service worker that listens to the PaymentRequestEvent. When a PaymentRequestEvent is received, the service worker opens a window to interact with the user.

      self.addEventListener('paymentrequest', function(e) {
        e.respondWith(new Promise(function(resolve, reject) {
          self.addEventListener('message', listener = function(e) {
            self.removeEventListener('message', listener);
            if (e.data.hasOwnProperty('name')) {
              reject(e.data);
            } else {
              resolve(e.data);
            }
          });

          e.openWindow("https://www.example.com/bobpay/pay")
          .then(function(windowClient) {
            windowClient.postMessage(e.data);
          })
          .catch(function(err) {
            reject(err);
          });
        }));
      });
      

The Web Payments Working Group plans to revisit these two examples.

Using the simple scheme described above, a trivial HTML page that is loaded into the payment handler window to implement the basic card scheme might look like the following:

<form id="form">
<table>
  <tr><th>Cardholder Name:</th><td><input name="cardholderName"></td></tr>
  <tr><th>Card Number:</th><td><input name="cardNumber"></td></tr>
  <tr><th>Expiration Month:</th><td><input name="expiryMonth"></td></tr>
  <tr><th>Expiration Year:</th><td><input name="expiryYear"></td></tr>
  <tr><th>Security Code:</th><td><input name="cardSecurityCode"></td></tr>
  <tr><th></th><td><input type="submit" value="Pay"></td></tr>
</table>
</form>

<script>
window.addEventListener("message", function(e) {
  var form = document.getElementById("form");
  /* Note: message sent from payment app is available in e.data */
  form.onsubmit = function() {
    /* See https://w3c.github.io/webpayments-methods-card/#basiccardresponse */
    var basicCardResponse = {};
    [ "cardholderName", "cardNumber","expiryMonth","expiryYear","cardSecurityCode"]
    .forEach(function(field) {
      basicCardResponse[field] = form.elements[field].value;
    });

    /* See https://w3c.github.io/payment-handler/#paymenthandlerresponse-dictionary */
    var paymentAppResponse = {
      methodName: "basic-card",
      details: details
    };

    e.source.postMessage(paymentAppResponse);
    window.close();
  }
});
</script>
      

Response

PaymentHandlerResponse dictionary

The PaymentHandlerResponse is conveyed using the following dictionary:
          dictionary PaymentHandlerResponse {
          DOMString methodName;
          object details;
          };
        

methodName attribute

The payment method identifier for the payment method that the user selected to fulfil the transaction.

details attribute

A JSON-serializable object that provides a payment method specific message used by the merchant to process the transaction and determine successful fund transfer.

The user agent receives a successful response from the payment handler through resolution of the Promise provided to the respondWith() function of the corresponding PaymentRequestEvent interface. The application is expected to resolve the Promise with a PaymentHandlerResponse instance containing the payment response. In case of user cancellation or error, the application may signal failure by rejecting the Promise.

If the Promise is rejected, the user agent MUST run the payment app failure algorithm. The exact details of this algorithm are left to implementers. Acceptable behaviors include, but are not limited to:

  • Letting the user try again, with the same payment handler or with a different one.
  • Rejecting the Promise that was created by PaymentRequest.show().

Respond to PaymentRequest Algorithm

When this algorithm is invoked with event and handlerResponsePromise parameters, the user agent MUST run the following steps:

  1. If event's dispatch flag is unset, then throw an "InvalidStateError" DOMException and abort these steps.
  2. If event.[[\respondWithCalled]] is true, throw an "InvalidStateError" DOMException and abort these steps.
  3. Set event.[[\respondWithCalled]] to true.
  4. Set the event's stop propagation flag and event's stop immediate propagation flag.
  5. Add handlerResponsePromise to the event's extend lifetime promises
  6. Increment the event's pending promises count by one.
  7. Upon rejection of handlerResponsePromise:
    1. Run the payment app failure algorithm and terminate these steps.
  8. Upon fulfillment of handlerResponsePromise:
    1. Let handlerResponse be the result of converting value to a PaymentHandlerResponse dictionary. If this throws an exception, run the payment app failure algorithm and terminate these steps.
    2. If handlerResponse.methodName is not present or not set to one of the values from event.methodData, run the payment app failure algorithm and terminate these steps.
    3. If handlerResponse.details is not present or not JSON-serializable, run the payment app failure algorithm and terminate these steps.
    4. Let serializeMethodName be the result of StructuredSerialize with handlerResponse.methodName. Rethrow any exceptions.
    5. Let serializeDetails be the result of StructuredSerialize with handlerResponse.details. Rethrow any exceptions.
    6. The user agent MUST run the user accepts the payment request algorithm as defined in [[!payment-request]], replacing steps 7 and 8 with these steps or their equivalent.
      1. Let methodName be the result of StructuredDeserialize with serializeMethodName. Rethrow any exceptions.
      2. Let details be the result of StructuredDeserialize with serializeDetails. Rethrow any exceptions.
      3. If any exception occurs in any of the above steps, then run the payment app failure algorithm and terminate these steps.
      4. Assign methodName to associated PaymentRequest's response.methodName.
      5. Assign details to associated PaymentReqeust's response.details.
  9. Upon fulfillment or rejection of handlerResponsePromise, queue a microtask to perform the following steps:
    1. Decrement the event's pending promises count by one.
    2. Let registration be the context object's relevant global object's associated service worker's containing service worker registration.
    3. If registration’s uninstalling flag is set, invoke Try Clear Registration with registration.
    4. If registration is not null, invoke Try Activate with registration.

The following example shows how to respond to a payment request:

      paymentRequestEvent.respondWith(new Promise(function(accept,reject) {
        /* ... processing may occur here ... */
        accept({
          methodName: "basic-card",
          details: {
            cardHolderName:   "John Smith",
            cardNumber:       "1232343451234",
            expiryMonth:      "12",
            expiryYear :      "2020",
            cardSecurityCode: "123"
           }
        });
      }));
          

[[!payment-request]] defines an ID that parties in the ecosystem (including payment app providers and payees) may use for reconciliation after network or other failures.

Security and Privacy Considerations

Information about the User Environment

User Consent before Payment

Secure Communications

Payment App Authenticity

The Web Payments Working Group is also discussing Payment App authenticity; see the (draft) Payment Method Manifest.

Supported Origin

Data Validation

Private Browsing Mode

Dependencies

This specification relies on several other underlying specifications.

Payment Request API
The terms payment method, PaymentRequest, PaymentResponse, supportedMethods, PaymentCurrencyAmount, paymentDetailsModifier, paymentDetailsInit, PaymentMethodData, ID, show(), and user accepts the payment request algorithm are defined by the Payment Request API specification [[!payment-request]].
ECMA-262 6th Edition, The ECMAScript 2015 Language Specification
The terms Promise, internal slot, TypeError, and JSON.stringify are defined by [[!ECMA-262-2015]].

The term JSON-serialize applied to a given object means to run the algorithm specified by the original value of the JSON.stringify function on the supplied object, passing the supplied object as the sole argument, and return the resulting string. This can throw an exception.

Payment Method Identifiers
The terms payment method identifier is defined by the Payment Method Identifier specification [[!payment-method-id]].
Basic Card Payment
The terms basic-card, supportedNetworks, and supportedTypes are defined in [[!payment-method-basic-card]].
HTML5
The terms global object, top-level browsing context, structured clone, event handler, event handler event type, trusted event, and user interaction task source are defined by [[!HTML5]].
RFC6454
The term origin is defined in [[!RFC6454]].
Writing Promise-Using Specifications
The terms upon fulfillment and upon rejection are defined by [[!PROMISES-GUIDE]].
DOM
The term fires (an event), dispatch flag, stop propagation flag, and stop immediate propagation flag are defined in [[!DOM4]].
Web IDL

When this specification says to throw an error, the user agent must throw an error as described in [[!WEBIDL]]. When this occurs in a sub-algorithm, this results in termination of execution of the sub-algorithm and all ancestor algorithms until one is reached that explicitly describes procedures for catching exceptions.

The algorithm for converting an ECMAScript value to a dictionary is defined by [[!WEBIDL]].

DOMException and the following DOMException types from [[!WEBIDL-LS]] are used:

  • "InvalidAccessError"
  • "InvalidStateError"
  • "NotAllowedError"
  • "NotFoundError"
  • "OperationError"
  • "SecurityError"
Secure Contexts
The term secure context is defined by the Secure Contexts specification [[!SECURE-CONTEXTS]].
Service Workers
The terms service worker, service worker client, ServiceWorkerRegistration, ServiceWorkerGlobalScope, handle functional event, extend lifetime promises,pending promises count, containing service worker registration, uninstalling flag, Try Clear Registration, Try Activate, and scope URL are defined in [[!SERVICE-WORKERS]].