Payment Request API [[!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-API]] 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.

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]]

Dependencies

This specification relies on several other underlying specifications.

Payment Request API
The terms payment method, PaymentRequest, PaymentResponse, supportedMethods, paymentDetailsModifier, paymentDetailsInit, PaymentMethodData, ID, show(), and user accepts the payment request algorithm are defined by the Payment Request API specification [[!PAYMENT-REQUEST-API]].
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 [[!METHOD-IDENTIFIERS]].
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]].
DOM
The term fires (an event) is defined in [[!DOM4]].
Web IDL

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

  • "InvalidStateError"
  • "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, and scope URL are defined in [[!SERVICE-WORKERS]].

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. Although from a permissions perspective there is a single Web app per origin, this specification provides mechanisms to origins for flexible structuring and display of instruments and wallets.
  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 for organizing the display and grouping of instruments and wallets supported by the payment handler.
  4. When the merchant (or other payee) calls the [[PAYMENT-REQUEST-API]] 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 and groups these choices according to 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-API]]) 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-API]]).

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. A PaymentWallet contains one or more PaymentInstruments and may be used to enhance the user experience (e.g., business wallet and personal wallet).

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

      interface PaymentManager {
        [SameObject] readonly attribute PaymentInstruments instruments;
        [SameObject] readonly attribute PaymentWallets wallets;
                              Promise<boolean>   requestPermission();
      };
      

The PaymentManager is used by payment apps to manage their associated wallets, 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.

wallets attribute

This attribute is used to group payment instruments (e.g., to group together "business account" payment instruments separately from "personal account" payment instruments). Developers can provide a name and icon for such a group. The use of this grouping mechanism by payment handlers is completely optional. If payment handlers use this grouping mechanism, then matching payment instruments that do not appear in any groups should still be presented to users by the user agent for selection.

Should the API support providing grouping information ("wallets") to the user agent? What should requirements be on user agents to display or provide for user interaction with this information?

requestPermission() method

The means for code requesting permission to handle payments is not yet defined.

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

PaymentInstruments interface

      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.

delete() method

When called, this method executes the following steps:

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

get() method

When called, this method executes the following steps:

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

keys() method

When called, this method executes the following steps:

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

has() method

When called, this method executes the following steps:

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

set() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. If the collection contains a PaymentInstrument with a matching instrumentKey, replace it with the PaymentInstrument in details.
    2. Otherwise, insert the PaymentInstrument in details as a new member of the collection and associate it with the key instrumentKey.
    3. Resolve p.
  3. Return p

clear() method

When called, this method executes the following steps:

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

PaymentInstrument dictionary

      dictionary PaymentInstrument {
        required DOMString name;
        sequence<ImageObjects> 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.

ImageObjects comes from the Web App Manifest specification. Should we reference the definition normatively, or make use of a simpler structure here?

PaymentWallets interface

      interface PaymentWallets {
          Promise<boolean>       delete(DOMString walletKey);
          Promise<PaymentWallet> get(DOMString walletKey);
          Promise<sequence<DOMString>>  keys();
          Promise<boolean>       has(DOMString walletKey);
          Promise<void>          set(DOMString walletKey, PaymentWallet details);
          Promise<void>           clear();
      };
      

Wallets are collections of payment instruments.

Where it appears, the walletKey argument is a unique identifier for the wallet.

delete() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. If the collection contains a PaymentWallet with a matching walletKey, remove it from the collection and resolve p with true.
    2. Otherwise, resolve p with false.
  3. Return p

get() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. If the collection contains a PaymentWallet with a matching walletKey, resolve p with that PaymentWallet.
    2. Otherwise, reject p with a DOMException whose value is "NotFoundError".
  3. Return p

keys() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. Resolve p with a sequence that contains all the walletKeys for the PaymentWallets contained in the collection, in original insertion order.
  3. Return p

has() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. If the collection contains a PaymentWallet with a matching walletKey, resolve p with true.
    2. Otherwise, resolve p with false.
  3. Return p

set() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. If the collection contains a PaymentWallet with a matching walletKey, replace it with the PaymentWallet in details.
    2. Otherwise, insert the PaymentWallet in details as a new member of the collection and associate it with the key walletKey.
    3. Resolve p.
  3. Return p

clear() method

When called, this method executes the following steps:

  1. Let p be a new promise.
  2. Run the following steps in parallel:
    1. Remove all PaymentWallets from the collection and resolve p.
  3. Return p

See issue 129.

PaymentWallet dictionary

      dictionary PaymentWallet {
          required DOMString name;
          sequence<ImageObject> icons;
          required sequence<DOMString> instrumentKeys;
      };
      
name member
The name member is a string that represents the label for this wallet 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 wallet when presented to the user for selection.
instrumentKeys member
The instrumentKeys member is a list of one or more instrumentKeys from PaymentManager.instruments, indicating which PaymentInstrument objects are associated with this Wallet, and should be displayed as being "contained in" the wallet. While it is not generally good practice, there is no restriction that prevents a PaymentInstrument from appearing in more than one Wallet.

Registration Example

The following example shows how to register a payment handler:

requestPermission() is not yet defined. The code below is based on one potential model, but this is likely to change.

        window.addEventListerner("DOMContentLoaded", async() => {
          const { registration } =
            await navigator.serviceWorker.register('/sw.js');
          if (!paymentManager) {
            return; // not supported, so bail out.
          }
          const state =
            await navigator.permissions.query({ name: "paymenthandler" });

          switch (state) {
            case "denied":
              return;
            case "prompt":
              // Note -- it's not clear how this should work yet; see Issue 94.
              const result = await registration.paymentManager.requestPermission();
              if (result === "denied") {
                return;
              }
              break;
          }
          // Excellent, we got it! Let's now set up the user's cards.
          await addInstruments(registration);
        }, { once: true });

        function addInstruments(registration) {
          const instrumentPromises = [
            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']
                }
              }),
            ];

            return Promise.all(instrumentPromises).then(() => {
              registration.paymentManager.wallets.set(
                "12a1b7e5-16c0-4c09-a312-9b191d08517b",
                {
                  name: "Acme Bank Personal Accounts",
                  icons: [
                           { src: "icon/lowres.webp",
                             sizes: "48x48",
                             type: "image/webp"
                           },
                           { src: "icon/lowres",
                             sizes: "48x48"
                           }
                         ],
                  instrumentKeys: [
                      "dc2de27a-ca5e-4fbd-883e-b6ded6c69d4f",
                      "c8126178-3bba-4d09-8f00-0771bcfd3b11",
                      "new-card"
                    ]
                });
             });
          };
     

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 deleted based on PR API issue 481.

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.

In issue 98 there has been push-back to always requiring display of instruments (e.g., on a mobile devices). User agents can incrementally show instruments. Or user agents can return an empty instrumentKey and it becomes the payment app's responsibility to display instruments to the user.

Grouping of Instruments

At times, the same origin may wish to group instruments with greater flexibility and granularity than merely "by origin." These use cases include:

A Wallet is a grouping of instruments for display purposes.

To enable developers to build payment apps in a variety of ways, we decouple the registration (and subsequent display) of instruments from how payment handlers respond to a PaymentRequestEvent. However, the user agent is responsible for communicating the user's selection in the event.

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).

Again related to issue 98: Should we require that, if displayed, individual instruments must be selectable? Or should we allow flexibility that instruments may be displayed, but selecting any one invokes all registered payment handlers? One idea that has been suggested: the user agent (e.g., on a mobile device) could first display the app-level icon/logo. Upon selection, the user agent could display the Instruments in a submenu.

Invocation

Once the user has selected an Instrument, the user agent fires a PaymentRequestEvent and uses the subsequent PaymentAppResponse to create a PaymentReponse for [[!PAYMENT-REQUEST-API]].

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 paymentrequest.

The PaymentRequestEvent

The PaymentRequestEvent represents a received PaymentRequest.

        [Exposed=ServiceWorker]
        interface PaymentRequestEvent : ExtendableEvent {
          readonly attribute DOMString topLevelOrigin;
          readonly attribute DOMString paymentRequestOrigin;
          readonly attribute DOMString paymentRequestId;
          readonly attribute FrozenArray<PaymentMethodData> methodData;
          readonly attribute PaymentItem total;
          readonly attribute FrozenArray<PaymentDetailsModifier> modifiers;
          readonly attribute DOMString instrumentKey;
          Promise<WindowClient> openWindow(USVString url);
          void respondWith(Promise<PaymentAppResponse>appResponse);
        };
      

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 method(s) 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 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.

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 PaymentAppResponse when the payment successfully completes.

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.

For DOM events compatibility, need to add a constructor, and the members of the corresponding dictionary need to match the attributes of the event.

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.

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.
    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 PaymentAppResponse as described in , 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 displays 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. If request.[[\state]] is not "interactive", then return a Promise rejected with a DOMException whose name is "InvalidStateError".
  4. Let url be the result of parsing the url argument.
  5. If the url parsing throws an exception, return a Promise rejected with that exception.
  6. If url is about:blank, return a Promise rejected with a TypeError.
  7. Let promise be a new Promise.
  8. Run these steps in parallel:
    1. Let newContext be a new top-level browsing context.
    2. Navigate newContext to url, with exceptions enabled and replacement enabled.
    3. If the navigation throws an exception, reject promise with that exception and abort these steps.
    4. If the origin of newContext is not the same as the service worker client origin associated with the payment handler, then:
      1. Reject promise with a DOMException whose name is "SecurityError".
      2. Abort these steps.
    5. Let client be the result of running the capture window client algorithm with newContext as the argument.
    6. 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.
    7. Set event.[[\windowClient]] to client.
    8. Resolve promise with client.
  9. Return promise.

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/webpayments-payment-apps-api/#sec-app-response */
    var paymentAppResponse = {
      methodName: "basic-card",
      details: details
    };

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

Response

PaymentAppResponse dictionary

The PaymentAppResponse is conveyed using the following dictionary:
          dictionary PaymentAppResponse {
          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 dictionary. The application is expected to resolve the Promise with a PaymentAppResponse 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().

Extention to User Accepts the Payment Request Algorithm

If the Promise is successfully resolved, the user agent MUST run the user accepts the payment request algorithm as defined in [[!PAYMENT-REQUEST-API]], replacing steps 6 and 7 with these steps or their equivalent:

  1. Set appResponse to the PaymentAppResponse instance used to resolve the PaymentRequestEvent.respondWith() Promise.
  2. If appResponse.methodName is not present or not set to one of the values from PaymentRequestEvent.methodData, run the payment app failure algorithm and terminate these steps.
  3. Create a structured clone of appResponse.methodName and assign it to response.methodName.
  4. If appResponse.details is not present, run the payment app failure algorithm and terminate these steps.
  5. Create a structured clone of appResponse.details and assign it to response.details.

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-API]] 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.

Data Validation

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