REST API Merge Proposal, Part 2: Content API

Hi everyone, it’s your friendly REST API team here with our second merge proposal for WordPress core. (WordPress 4.4 included the REST API Infrastructure, if you’d like to check out our previous merge proposal.) Even if you’re familiar with the REST API right now, we’ve made some changes to how the project is organised, so it’s worth reading everything here.

(If you haven’t done so already, now would be a great time to install the REST API and OAuth plugins from WordPress.org.)

A brief history of the REST API

The REST API was created as a proof-of-concept by Ryan McCue (hey, that’s me!) at the WordPress Contributor Summit in 2012, but the project kicked off during the 2013 Google Summer of Code. The end result was Version 1.0, which grew into a community supported initiative that saw adoption and provided for a solid learning platform. The team used Version 1 to test out the fundamental ideas behind the API, and then iterated with Version 2, which made some major breaking changes, including explicit versioning, the introduction of namespacing for forwards compatibility, and a restructure of the internals. Version 2 also led to the infrastructure of the REST API being committed to WordPress core in 4.4.

This infrastructure is the core of the REST API, and provides the external interface to send and receive RESTful HTTP requests. Since shipping in 4.4, the infrastructure is now used by WordPress Core for oEmbed responses, and by plugins like WooCommerce and Jetpack, enabling anyone to create their own REST API endpoints.

The team has also been hard at work on the API endpoints. This has included core changes to WordPress to support the API, including deeper changes to both settings and meta.

Today the REST API team is proposing the inclusion of a collection of endpoints that we term the “Content API” into WordPress Core.

Proposals for Merge

Content Endpoints

For WordPress 4.7 the API team proposes to merge API endpoints for WordPress content types. These endpoints provide machine-readable external access to your WordPress site with a clear, standards-driven interface, allowing new and innovative apps for interacting with your site. These endpoints support all of the following:

  • Content:
    • Posts: Read and write access to all post data, for all types of post-based data, including pages and media.
    • Comments: Read and write access to all comment data. This includes pingbacks and trackbacks.
    • Terms: Read and write access to all term data.
    • Users: Read and write access to all user data. This includes public access to some data for post authors.
    • Meta: Read and write access to metadata for posts, comments, terms, and users, on an opt-in basis from plugins.
  • Management:
    • Settings: Read and write access to settings, on an opt-in basis from plugins and core. This enables API management of key site content values that are technically stored in options, such as site title and byline.

This merge proposal represents a complete and functional Content API, providing the necessary endpoints for mobile apps and frontends, and lays the groundwork for future releases focused on providing a Management API interface for full site administration.

Content API endpoints support both public and authenticated access. Authenticated access allows both read and write access to anything your user has access to, including post meta and settings. Public access is available for any already-public data, such as posts, terms, and limited user data for published post authors. To avoid potential privacy issues we’ve taken pains to ensure that everything we’re exposing is already public, and the API uses WordPress’ capability system extensively to ensure that all data is properly secured.

Just like the rest of WordPress, the Content API is fully extensible, supporting custom post meta, as well as allowing more complex data to be added via register_rest_field. The API is built around standard parts of WordPress, including the capability system and filters, so extending the API in plugins should feel as familiar to developers as extending any other part of WordPress.

This Content API is targeted at a few primary use cases, including enhancing themes with interactivity, creating powerful plugin interfaces, building mobile and desktop applications, and providing alternative authoring experiences. We’ve been working on first-party examples of these, including a mobile app using React Native and a liveblogging web app, as well as getting feedback from others, including WIRED, the New York Times, and The Times of London. Based on experience building on the API, we’ve polished the endpoints and expanded to support settings endpoints, which are included as the first part of the Management API.

Authentication

The API Infrastructure already in WordPress core includes support for regular cookie-based authentication. This is useful for plugins and themes that want to use the API, but requires access to cookies and nonces, and is hence only useful for internal usage.

To complement the Content Endpoints, for WordPress 4.7 the API team also proposes merging the REST API OAuth 1 server plugin into WordPress Core. This plugin provides remote authentication via the OAuth 1 protocol, allowing remote servers and applications to interact securely with the WordPress API.

OAuth is a standardised system for delegated authorisation. With OAuth, rather than providing your password to a third-party app, you can authorise it to operate on your behalf. Apps are also required to be registered with the site beforehand, which gives site administrators control over third-party access. Access to these apps can be revoked by the user if they are no longer using the app, or by a site administrator. This also allows apps with known vulnerabilities to have compromised credentials revoked to protect users.

We’ve chosen OAuth 1 over the newer OAuth 2 protocol because OAuth 1 includes a complex system for request signing to ensure credentials remain secure even over unsecured HTTP, while OAuth 2 requires HTTPS with a modern version of TLS. While it is strongly encouraged for sites to use HTTPS whenever possible (Let’s Encrypt makes it easier than ever to do so), WordPress itself does not require HTTPS and we do not believe WordPress should make HTTPS a requirement for using the API. The additional complexity that OAuth 1 adds can be easily supported by a library, and many such libraries already exist in most programming languages. OAuth 1 remains supported around the web, including for the Twitter API, and we also provide extensive documentation on using it.

Authentication Beyond 4.7

One issue with OAuth over direct username and password authentication is that it requires applications to be registered on the site. For centralized OAuth servers this wouldn’t be a problem, but the distributed nature of WordPress installations makes this tough to handle: your application must be independently registered with every WordPress site it connects to. If you’ve ever had to create a Twitter or Facebook app just to use an existing plugin on your site, you’ll know this can be a less-than-optimal experience for users.

To solve this distribution problem, we’ve created a solution called brokered authentication. This allows a centralised server (called the “broker”) to handle app registration and to vouch for these apps to individual sites. It simplifies app registration by allowing app developers to register once for all sites, and improves security by allowing the broker to vet applications and revoke them across the entire network. The system is designed to allow multiple brokers; while the main broker is run at apps.wp-api.org, organisations can run their own broker for internal usage, and developers can run a broker locally for testing.

While the broker system has been running live at apps.wp-api.org for months, we want to stay conservative in our approach to the API, especially where security is concerned. We are therefore proposing brokered authentication for WordPress 4.8 to ensure we have further time to continue testing and refining the broker system. In addition, this will require an installation of the broker on a centralised server to act as the canonical broker for out-of-the-box WordPress. While apps.wp-api.org is currently acting in this role, this is currently hosted by a third-party (Human Made) on behalf of the API team. For long-term usage the broker should instead be hosted on WordPress.org, alongside the existing plugin and theme repositories. This migration will take time but we remain committed to continuing to develop and support the broker.

After Merge

After merging the REST API, the team plans to continue developing the API as before. We expect that integrating the REST API into WordPress core will bring additional feedback, and we plan on incorporating this feedback through the rest of the 4.7 cycle.

During the remaining parts of this release cycle and through into the 4.8 cycle, additional work will go into other parts of the API. This includes further work and refinement on the broker authentication system, including work on WordPress.org infrastructure. Additionally, we plan to continue working on the Management API endpoints, including theme and appearance endpoints to support the Customiser team. Both of these components will be maintained as separate feature projects on GitHub until they’re ready for merge into core.

The team remains committed to supporting the API in core, and the Content API will switch from GitHub to Trac for project management and contributions. This same process occurred for the API Infrastructure in WordPress 4.4.

Reviews and Feedback

With this merge proposal, we’re looking for feedback and review of the project. In particular, we’re focussing on feedback on the security of the API and OAuth projects, and are also reaching out to specific people for reviews. (We take the security of the API seriously, and bug reports are welcomed on HackerOne at any time.) Design and accessibility reviews for the OAuth authorisation UI are also welcomed to ensure we maintain the high standards of WordPress core.

Both the REST API plugin and the OAuth plugin are available on WordPress.org, and issues can be reported to the GitHub tracker for the API and the OAuth plugin respectively. We have released a final beta (Beta 15 “International Drainage Commission”) which includes the meta and settings endpoints.

With Love from Us

As always, this is a merge proposal, and is not final until 4.7 is released. We’re eager to hear your thoughts and feedback; the comments below are a perfect place for that, or you can pop along to one of our regular meetings. We’re also always available in the #core-restapi room on Slack.

We’d like to thank every single one of our contributors, including 88 contributors to the main repository and 23 contributors to the OAuth repository. Particular thanks goes to my (@rmccue) wonderful co-lead Rachel Baker (@rachelbaker), our 2.0 release leads Daniel Bachhuber (@danielbachuber) and Joe Hoyle (@joehoyle), and our key contributors for the 4.7 cycle: Adam Silverstein (@adamsilverstein), Brian Krogsgard (@krogsgard), David Remer (@websupporter), Edwin Cromley (@chopinbach), and K. Adam White (@kadamwhite). Thanks also to the core committers helping us out through the 4.7 cycle, including Aaron D. Campbell (@aaroncampbell) and Aaron Jorbin (@aaronjorbin), and to the fantastic release lead, Helen Hou-Sandí (@helen).

Thanks also to everyone who has used the REST API, and to you for reading this. We built the REST API for you, and we hope you like it.

With love, The REST API Team