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title	description	url	paginate
Web Payment APIs	A short talk on Web Payment APIs	https://captnemo.in/talks/webpayments/	true

Web Payment APIs

- nemo (RFCs We Love, May 2020)

`whoami`

Nemo me@captnemo.in
Tech/Security @ Razorpay

webpayments

The goal is to create a safe, decentralized system and a set of open, patent and royalty-free specifications that allow people on the Web to send each other money as easily as they exchange instant messages and e-mail today.

W3C

ActivityPub
CGI
CSS
DOM
HTML
RDF
SOAP
SPARQL
SVG
XHTML
XML
XPath

demo

Before we start, let's do a quick demo of how it all comes together.

specifications*

Payment Request API

Payment Method Identifiers

Payment Handler API

Payment Method Manifest

See github.com/w3c/webpayments/wiki for a complete list

* working drafts

specifications*

Payment Request API: how to initiate a payment
Payment Method Identifiers: what is a payment method?
Payment Method Manifest: definition of a payment method
Payment Handler API: how a payment method is processed?

the talk

Try to understand how we can complete a payment entirely from within your browser without relying on any proprietary APIs (as a processor/merchant), and yet being compatible with any payment instrument.

definitions

The payment method: the means that the payer uses to pay the payee (e.g., a basic card payment). They are uniquely identified via a Payment Method Identifier (PMI)

The payment method provider establishes the ecosystem to support that payment method.

The details of how to fulfill a payment request for a given payment method is an implementation detail of a payment handler, which is a Web application that can handle a request for payment on behalf of the user.

examples

payment method: Paytm Wallet Account, UPI, Card, Gift Card, Voucher Code, Bitcoin.

Payment Method Identifier: https://paytm.com, https://npci.org.in/upi, basic-card

payment method provider: Razorpay, Stripe, PayPal, NPCI/UPI, your-bank-goes-here

Payment Method Identifier

URL-based payment method identifier (say, https://bitcoincore.org/ or https://pay.wechat.com).
or a standardized payment method identifier (currently only basic-card is on the registry).

humanized: how to identify and categorize various payment methods?

Payment Method Manifest

allows the curators of a defined payment method or owners of a proprietary payment method to authorize (via a manifest file) which payment handlers may be used to fulfill the payment method.

humanized: defines the "how-to-process" action of a specific payment method. The one for basic-card is standardized in a specification already.

How to get to the manifest?

GET / HTTP/2
Host: alicepay.com

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

You can alternatively just redirect from your PMI URL, or serve the JSON directly on the PMI URL

What's inside a Manifest?

A payment method manifest tells the user-agent "how to process payments for a particular method".

URL: https://alicepay.com/pay/payment-manifest.json

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

what happens?

user-agent can go next to https://alicepay.com/pay/app/webappmanifest.json to install the AlicePay application.

supported_origins defines which origins can be trusted to install an application for this payment method.

What's inside a Manifest (1)

{
  //...
  "supported_origins": [
    "https://beta.alicepay.com",
    "https://bobpay.com"
  ]
}

A payment application hosted at either alicepay.com, beta.alicepay.com, or bobpay.com is now authorized for the payment method https://alicepay.com.

What's inside a Manifest (2)

{
  //...
  "supported_origins": "*"
}

any third party is allowed to support the payment method.

recap

So far, the user-agent has done the following:

seen a payment-method (we haven't gotten to how)
discovered the payment method manifest URL
parsed the payment method manifest to determine the webapp manifest URL
fetched the webapp manifest URL
installed the payment method's application(s)

The application installation is based on W3C's Web App Manifest specification.

What's inside the Payment Handler?

A PaymentManager is an additional attribute to the ServiceWorker specification, which allows a piece of code to run/listen in background in your browser, even after the tab is closed.

PaymentManager {
  instruments = PaymentInstruments {
      delete(instrumentKey)
      get(instrumentKey)
      keys()
      has(instrumentKey);
      set(instrumentKey, PaymentInstrument details);
      clear();
  }
  userHint
}

Payment Instrument

Defines what all different instruments a user might have registered against this method (Multiple wallets, bank accounts, cards etc).

PaymentInstrument {
  // Visa Card ending in **1214
  name;
  // Visa icon
  icons;
  // PMI
  method;
  // Can be used to restrict card usage by network for eg.
  capabilities;
}

PaymentHandler API

A payment handler listens on the PaymentRequestEvent, and returns a PaymentHandlerResponse once done.

PaymentHandlerResponse {
  methodName // PMI
  details {}
  payerName;
  payerEmail;
  payerPhone;
  shippingAddress;
  shippingOption;
}

Payment Handler

Each payment handler defines:

Steps to check if a payment can be made (listen to CanMakePaymentEvent)
Steps to respond to a payment request: (PaymentRequestEvent)

The structure of this object is specific to each payment method.

Steps for when a user changes payment method (optional) (PaymentRequestDetailsUpdate)

Steps that describe how to handle the user changing payment method or monetary instrument (e.g., from a debit card to a credit card)

Payment Request API

Native Applications?

You can declare support for native applications via a few non-standardized changes to the payment method manifest:

{
  "related_applications": [{
    "platform": "play",
    "id": "com.bobpay.app",
    "min_version": "1",
    "fingerprints": [{
      "type": "sha256_cert",
      "value": "92:5A:39:05:C5:B9:EA:BC:71:48:5F:F2"
    }],
    "url": "https://play.google.com/store/apps/details?id=com.bobpay.app"
  }]
}

Native applications (2)

Instead of using service-workers now, your payment application can rely on platform-specific APIs for the same purpose. Android uses Intents, for eg.

In the Wild

Google Pay is already using Payments API to support cross-platform Payments, by declaring a new "https://google.com/pay" payment method.
Apple Pay runs in browsers using the Payment Request API.
So does Samsung Pay
Payment processors are adding support for it: Stripe, BrainTree, Worldline
Facebook implements it within their in-app browser for the Mobile SDK.

Future Scope

Installing a payment app is clunky, maybe we can just install the service-worker directly.
Lots of work happening towards standardization of non-card payments (such as SEPA).

12 KiB Raw Blame History

Web Payment APIs

whoami

webpayments

W3C

demo

specifications*

specifications*

the talk

definitions

examples

Payment Method Identifier

Payment Method Manifest

How to get to the manifest?

What's inside a Manifest?

what happens?

What's inside a Manifest (1)

What's inside a Manifest (2)

recap

What's inside the Payment Handler?

Payment Instrument

PaymentHandler API

Payment Handler

Payment Request API

Native Applications?

Native applications (2)

In the Wild

Future Scope

References

12 KiB

Raw Blame History

`whoami`