Payment Method Manifest

Status of this document

HEAD / HTTP/2
Host: alicepay.com
User-Agent: Mellblomenator/9000

HTTP/2 204
Link: </pay/payment-manifest.json>; rel="payment-method-manifest"

{
  "default_applications": ["https://alicepay.com/pay/app/webappmanifest.json"],
  "supported_origins": [
    "https://bobpay.xyz",
    "https://alicepay.friendsofalice.example"
  ]
}

2. Manifest format

A valid payment method manifest file is a UTF-8 encoded file containing contents parseable as a JSON object. The resulting JSON object must contain at most two items, with the possible keys "default_applications" and "supported_origins".

The value of the default_applications key, if present, must be a non-empty JSON array. Each item in the array must be an absolute-URL string such that the resulting parsed URL's scheme is "https".

The value of the supported_origins key, if present, must be either the string "*", or a non-empty JSON array. In the latter case, each item in the array must be an absolute-URL string that represents an HTTPS origin. Formally, the string must be equal to the serialization of the resulting parsed URL's origin.

Web developers must ensure that all of their payment method manifests are valid.

As with all conformance requirements on the contents of files, these are web-developer facing, and not implementer-facing. The exact processing model (given in §3 Processing model) governs how implementers process all payment method manifest files, including invalid ones.

{
  "default_applications": ["https://alicepay.com/pay/app/webappmanifest.json"],
  "created_by": "Alice",
  "created_in": "Wonderland"
}

3. Processing model

3.1. Modifications to Payment Request API

This specification integrates with the rest of the Payment Request ecosystem by modifying the PaymentRequest(methodData, details, options) constructor. It adds the following steps, before the algorithm completes and returns the newly-constructed PaymentRequest object. In what follows, let request be the PaymentRequest instance being constructed. [PAYMENT-REQUEST]

1. Let identifiers be a list consisting of the first item of each pair in request.[[serializedMethodData]].

2. Let client be the current settings object.

3. Ingest payment method manifests given identifiers and client.

These steps are what kicks off the whole process. The rest of §3 Processing model is concerned with defining how this process eventually leads to new payment apps being available for the user.

As this specification gains multi-implementer interest, we anticipate moving this section into the Payment Request API specification itself, instead of maintaining a monkeypatch here.

3.2. Ingesting payment method manifests

Given a list of payment method identifiers identifiers, as well as an environment settings object client, the user agent may run the following steps, to ingest payment method manifests:

1. Fetch payment method manifests, given identifiers and client, and wait for this to asynchronously complete with manifestsMap. If the result is failure, return.

2. For each identifier → manifest of manifestsMap:

   1. Let parsed be the result of validating and parsing manifest. If this returns failure, continue.

   2. For each url in parsed’s default applications:

      1. Fetch the web app manifest at url given client, and wait for it to asynchronously complete with webAppManifestString. If the result is failure, continue.

      2. Let webAppManifest be the result of running the steps for processing a web app manifest given webAppManifestString.

         The steps for processing a web app manifest are very forgiving and will return empty objects or objects missing crucial fields instead of failing. User agents will need to separately validate the processed web app manifest to ensure it contains enough data for their purposes in the next step.

      3. In a user-agent-specific way, use the resulting processed web app manifest webAppManifest to install any applicable payment apps for the payment method identified by identifier.

         In the future, the plan is for there to be a user-agent-independent way to use the resulting processed web app manifest, by consulting its serviceworker field and using that to install a web-based payment app conforming to the Payment Handler API specification. [PAYMENT-HANDLER]

   3. Associate the supported origins to identifier so that the user agent can use it in the future to determine what third-party payment apps can be displayed for the payment method identified by identifier.

3.3. Fetching payment method manifests

To fetch payment method manifests, given a list of JavaScript strings supportedMethods and an environment settings object client, perform the following steps. This algorithm will asynchronously complete with a map (possibly empty) from URLs to byte sequences, mapping payment method identifiers to the contents of the corresponding manifest.

1. Let identifierURLs be an empty list.

2. For each string of supportedMethods:

   1. Let identifierURL be the result of basic URL parsing string. If the result is failure, continue.

      The result will be failure for any payment method identifier that is not a URL-based payment method identifier, i.e. for a standardized payment method identifier.

   2. If validating identifierURL returns false, continue.

   3. Optionally, continue.

      This step allows implementations to skip any of the provided payment method identifiers for user-agent-specific reasons. §4 Security and privacy considerations discusses some reasons why user agents might prefer to only ingest certain identifiers.

   4. Append identifierURL to identifierURLs.

3. Let manifestsMap be an empty map.

4. For each identifierURL of identifierURLs:

   1. Let identifierRequest be a new request whose method is `HEAD`, url is identifierURL, client is client, mode is "cors", credentials mode is "omit", and redirect mode is "error".

   2. Fetch identifierRequest. To process response with the response identifierResponse:

      1. If identifierResponse is a network error or identifierResponse’s status is not an ok status, continue.

      2. Let linkHeaders be the result of extracting header list values given `Link` and identifierResponse’s header list.

      3. Let manifestURLString be null.

      4. For each linkHeader of linkHeaders:

         1. Parse linkHeader according to the link-value production. If it cannot be parsed, continue. [RFC8288]

         2. If the parsed header contains a parameter whose name is an ASCII case-insensitive match for the string "rel" and whose value is an ASCII case-insensitive match for the string "payment-method-manifest", then set manifestURLString to the string given by the URI-Reference production in the parsed header, and break.

      5. If manifestURLString is not null, then:

         1. Let manifestURL be the result of basic URL parsing manifestURLString with base URL given by identifierResponse’s url. If the result is failure, continue.

         2. If manifestURL’s scheme is not "https", continue.

         3. Let manifestRequest be a new request whose url is manifestURL, client is client, mode is "cors", credentials mode is "omit", and redirect mode is "error".

         4. Fetch manifestRequest. To process response end-of-body with the response manifestResponse:

            1. If manifestResponse is a network error or manifestResponse’s status is not an ok status, continue.

            2. Let body be manifestResponse’s body.

            3. If body is null, continue.

            4. Let reader be the result of getting a reader from body.

            5. Let promise be the result of reading all bytes from body with reader.

            6. Upon fulfillment of promise with a byte sequence bytes, set manifestsMap[identifierURL] to bytes.

5. Once all ongoing fetch algorithms initiated by the above steps are complete, including the specified process response and process response end-of-body steps, asynchronously complete this algorithm with manifestsMap.

3.4. Validating and parsing payment method manifests

A parsed payment method manifest is a struct containing two fields:

default applications

An ordered set of URLs, possibly empty

supported origins

Either the string "*", or an ordered set of origins

To validate and parse a byte sequence bytes purporting to contain a payment method manifest, perform the following steps. The result will either be a parsed payment method manifest, or failure.

1. Let parsed be the result of parsing JSON from bytes given bytes, in a user-agent defined JavaScript realm. If this throws an exception, return failure.

2. If Type(parsed) is not Object, return failure.

3. Let defaultApps be an empty ordered set.

4. Let defaultAppsValue be Get(parsed, "default_applications").

5. If defaultAppsValue is not undefined:

   1. If IsArray(defaultAppsValue) is false, return failure.

   2. Let defaultAppsList be CreateListFromArrayLike(defaultAppsValue, « String »). If this throws an exception, return failure.

   3. If the size of defaultAppsList is 0, return failure.

   4. For each defaultAppString in defaultAppsList:

      1. Let defaultAppURL be the result of basic URL parsing defaultAppString. If the result is failure, return failure.

      2. If defaultAppURL’s scheme is not "https", return failure.

      3. Append defaultAppURL to defaultApps.

6. Let supportedOrigins be an empty ordered set.

7. Let supportedOriginsValue be Get(parsed, "supported_origins").

8. If supportedOriginsValue is "*", set supportedOrigins to "*".

9. Otherwise, if supportedOriginsValue is not undefined:

   1. If IsArray(supportedOriginsValue) is false, return failure.

   2. Let supportedOriginsList be CreateListFromArrayLike(supportedOriginsValue, « String »). If this throws an exception, return failure.

   3. If the size of supportedOriginsList is 0, return failure.

   4. For each supportedOriginString in supportedOriginsList:

      1. Let supportedOriginURL be the result of basic URL parsing supportedOriginString. If the result is failure, return failure.

      2. If supportedOriginURL’s scheme is not "https", return failure.

      3. If supportedOriginURL’s username or password are not the empty string, return failure.

      4. If supportedOriginURL’s path's size is not 0, return failure.

      5. If supportedOriginURL’s query or fragment are not null, return failure.

      6. Append supportedOriginURL’s origin to supportedOrigins.

10. Return a new parsed payment method manifest with default applications given by defaultApps and supported origins given by supportedOrigins.

{
  "default_applications": ["https://alicepay.com/pay/app/webappmanifest.json"],
  "supported_origins": []
}

3.5. Fetching web app manifests

Because the determination of payment apps happens independent of any embedding HTML document, the procedure for obtaining a web app manifest that gives information about a default payment app is different from the usual steps for obtaining a web app manifest.

To fetch the web app manifest for a default payment app, given a URL url and an environment settings object client, perform the following steps. This algorithm will asynchronously complete with either a scalar value string or failure.

1. Let request be a new request whose url is url, client is client, mode is "cors", credentials mode is "omit", and redirect mode is "error".

2. Fetch request. To process response end-of-body with the response response:

   1. If response is a network error or response’s status is not an ok status, asynchronously complete this algorithm with failure.

   2. Let body be response’s body.

   3. If body is null, asynchronously complete this algorithm with failure.

   4. Let reader be the result of getting a reader from body.

   5. Let promise be the result of reading all bytes from body with reader.

   6. Upon fulfillment of promise with a byte sequence bytes, asynchronously complete this algorithm with the result of UTF-8 decoding bytes.

   7. Upon rejection of promise, asynchronously complete this algorithm with failure.

4. Security and privacy considerations

Ingesting payment method manifests might reveal information to a payment service about the activity of an end user. For example, a payment method that is only supported on one website might allow that payment provider to discover the IP addresses of users who visit that website.

One way to mitigate this is to fetch the manifests only for the payment apps that the user has installed or has explicitly expressed interest in. This confines the risk to only sharing the user’s IP address with those parties.

5. IANA considerations

5.1. The payment-method-manifest link relation

This registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Relation name

payment-method-manifest

Description

Links to a payment method manifest, which describes a specific payment method within the Web Payments ecosystem.

Reference

https://w3c.github.io/payment-method-manifest/

Notes

See §3.3 Fetching payment method manifests for the specific manner in which such links are expected to be fetched, and §3.2 Ingesting payment method manifests for the larger context in which they are used.

Acknowledgments

§3 Processing model is based heavily on algorithms originally outlined by Rouslan Solomakhin.