This document outlines the Web Payments ecosystem by introducing readers to the goals of the ecosystem, messages, roles, and information flow in the system. Links to specifications that define each aspect of the ecosystem in more detail are also included for implementers.

Introduction

This document outlines the Web Payments ecosystem. It starts by highlighting the goals of the ecosystem, then covers the primary types of messages exchanged and the roles of participants in the system. An example use case is then used to demonstrate how roles in the system communicate. Finally, specifications that detail each aspect of the ecosystem in more detail are also provided for implementers.

Web Payments Goals

The Web Payments ecosystem strives to support fundamental Web principles by:

Adhering to Web architecture fundamentals
Supporting network and device independence
Providing for payers and payees with differing physical and cognitive abilities
Being machine-readable where possible to enable automation and engagement of non-human entities
Protecting the privacy of all participants

In addition to the fundamental Web principles above, the Web Payments ecosystem also strives to:

Improve the interface experience for all stakeholders
Provide stakeholders with unencumbered knowledge and choice when undertaking a payment
Support a wide spectrum of security and privacy needs to meet industry expectations
Support existing payment schemes while enabling new ones
Encourage efficient settlement
Facilitate compliance with legal and regulatory obligations
Enable monetization on the spectrum of Web to native apps
Bridge distributed value networks

The Structure of Payment Messages

A payment request is composed of the following parts:

Payment Methods: The methods of payment that may be used for processing the payment request. Examples include: credit card, direct debit, SEPA Credit Transfer, and Bitcoin.
Payment Details: Specific information pertaining to the transaction. Examples include: price, transaction reference number, and items being purchased.
Payment Options: A set of information that needs to be collected from the payer in order for the transaction to be fulfilled. Examples include: shipping options, requests for shipping address, and requests for contact information.

A concern has been raised over the structure of a payment request, notably that there are other forms of messages that may be initiated by a payer. There is currently a proposal to modify payment request to a more generalized "payment instruction" that would be capable of expressing other messages like subscriptions, preauthorizations, refunds, and other sorts of payment-related instructions.

A payment response is composed of the following parts:

Payment Method: The selected mechanism that was used for processing the payment. Examples include: credit card, ACH, SEPA, and Bitcoin.
Transaction Details: Specific information pertaining to the transaction. Examples include: transaction reference number, price, and items purchased.
Response Details: Information that pertains to the result of processing the payment including all information requested in the initial payment request. Examples include: selected shipping option, shipping address, and contact email.

Roles in the Ecosystem

There are a number of roles and interactions in the Web Payments ecosystem. A role is an abstraction that might be implemented in many different ways. The separation of roles suggests likely interfaces and/or protocols for standardization. The following roles exist in the Web Payments ecosystem:

Payer: An entity transmitting value to the Payee.
Payee: An entity receiving value from the Payer.
Mediator: Routes payment requests between the Payee and the Payment App.
Payment App: Processes payment requests sent via the Mediator and returns payment responses to the Mediator. It may communicate with Payment Networks to execute a payment instruction or it may return data so that another entity can execute a payment instruction.
Payment Network: A system that is responsible for transferring value from one entity to another.

As the diagram above depicts, the Web Payments ecosystem separates the following concerns:

The role that creates the payment request (Payee) is separated from the role that routes the payment request to the entity that will process it (Mediator).
The role that routes the payment request (Mediator) is separated from the role that processes the payment request (Payment App).
The role that processes the payment request/response (Payment App/Payee) is separated from the role that transfers the value associated with the request/response (Payment Network).

An Exemplary Use Case

In order to understand how all of the actors and roles in the ecosystem interact, consider the following use case:

Quinn would like to purchase a new laptop using her new security-enhanced credit card.

Payer Registers Payment App

Note that this section is currently speculative and will be updated once consensus forms around a corresponding payment application registration specification, which is currently under development.

In order for Quinn (Payer) to use her new security-enhanced credit card, she must enroll it via her bank's website (Payment App).

Payer Makes a Purchase

Quinn (Payer) finds the laptop she wants on a website (Payee). She clicks "Buy", selects the information necessary to complete the transaction, and is notified that her purchase is successful and is on its way.

Implementing Web Payments Software

There are a number of specifications that are of interest to developers implementing portions of the ecosystem outlined in this document.

Payment Methods and Basic Card: Details how payment methods are identified and how new payment methods are specified.
Web Payment Applications: Specifies how messages are exchanged between a payment app and a mediator.
Web Payments HTTP Messages: Message types and content used by the Web Payments HTTP API.
Web Payments HTTP API: Specifies how Web Payments HTTP Messages are exchanged via an HTTP client and server.
Web Payments Browser API: Specifies how messages are transmitted and processed via a Web browser.