Backdrop Federation

Enables ActivityPub federation for Backdrop CMS, connecting your site to the Fediverse. Fediverse users can follow the site and receive posts in their feeds. Replies, likes, and boosts from the Fediverse are reflected back on the site.

The core module implements an outbound publisher model: the site acts as an ActivityPub actor that broadcasts content to followers. An optional sub-module, Backdrop Federation Follow, extends this to two-way federation by allowing the site to follow remote accounts and receive their posts in a local feed. A "Fediverse Feed" block is available to display the incoming feed.

Status

We have installed and tested the module under limited server conditions. Other than the issues reported in the issue queue, we expect that everything is working. However, this module needs additional testing and feedback.

We would really appreciate some feedback on the user interface.
The blocklist feature needs additional testing.
We anticipate some people may experience problems depending upon server configuration. Let us know about your experiences.

Limitations

This module federates a content-publishing site rather than running a social network, which shapes what it can and cannot do.

The most significant constraint is the single-actor model — the entire site presents itself as one identity, so individual authors have no Fediverse presence of their own. Only a subset of ActivityPub's activity vocabulary is supported: the site cannot originate likes, boosts, or replies, and outgoing posts lack hashtag and mention metadata, limiting their discoverability on remote servers. Everything published is effectively public, with no support for followers-only, unlisted, or direct-message visibility.

Posts received from followed accounts are displayed more plainly than in a native Fediverse client. Inline images are rendered, but link previews and OpenGraph images are not fetched, so posts that depend on a rich preview card will appear as bare text links.

Finally, delivery is best-effort rather than guaranteed — if a remote inbox is down at publish time and cron misses it, the post is not delivered.

For a site whose primary purpose is publishing content to an audience that includes Fediverse users, these are reasonable trade-offs. For anything resembling a social platform, they would be fundamental gaps.

Installation

Install this module using the official Backdrop CMS instructions. Bugs and feature requests should be reported in the Issue Queue.

Getting Started

1. Configure the site actor

Go to Administration › Configuration › Web services › Backdrop Federation and open the Settings tab.

Set an actor username — this becomes the local part of your Fediverse handle (e.g. news gives you @news@yoursite.com)
Add a display name and bio that will appear on your profile when viewed from Mastodon or other Fediverse apps
Select which content types should be federated — only published nodes of these types will be broadcast to followers
Save the settings

2. Verify your handle is discoverable

Your site's Fediverse handle is @username@yourdomain.com. Search for it from any Mastodon account — if your profile appears, WebFinger is working correctly and the site is ready to federate.

Note: The site must be publicly accessible over HTTPS. Federation will not work on localhost or behind a firewall.

3. Follow the site and publish a post

Follow your site's handle from a Mastodon or other Fediverse account. The follower should appear under the Followers tab within a few seconds. Then publish or re-save a node of a federated content type and check that it appears in your Fediverse feed.

Tip: If you published content before any followers existed, use the Re-deliver button on the Settings tab to re-send all outbox entries to your current followers.

4. Try the Follow sub-module (optional)

Enable Backdrop Federation Follow to follow remote Fediverse accounts and receive their posts on your site. Once enabled, two new tabs appear on the settings page:

Following — enter a @user@domain handle and click Follow; the module resolves the handle and sends a follow request automatically
Feed — browse posts received from followed accounts

To display the feed on your site, add the Fediverse Following Feed block to any layout region via Structure › Layouts. You can also use the Views module to build a custom public-facing feed page using the "Fediverse Feed Post" base table.

Included Sub-modules

Sub-module	Purpose
Backdrop Federation Follow	Follow remote Fediverse accounts and display their posts in a local feed

Sub-modules are located inside the backdrop_federation/ directory and can be enabled independently at admin/modules.

Features

Site actor — the site presents itself as an ActivityPub Application actor discoverable by @username@domain handle
WebFinger — resolves acct:name@domain handles so remote servers can discover the actor
NodeInfo — advertises software name, version, and usage statistics to the Fediverse
Content federation — selected content types are automatically broadcast when nodes are published, updated, or unpublished
Immediate delivery — posts are delivered to follower inboxes synchronously on node save, with cron as a fallback
Per-type field mapping — choose which text field is used as the post body for each content type
Per-type object type — federate each content type as a Note or Article
Content negotiation — node URLs respond with ActivityPub JSON when requested with an appropriate Accept header, allowing remote servers to fetch and verify notes by URL
Follower management — accepts Follow activities, stores followers, and sends signed Accept responses
Shared inbox support — uses a follower's shared inbox when available to reduce delivery requests
Re-deliver button — re-queues all outbox entries to current followers from the admin UI
Outbox debug view — browse outgoing activities and inspect their raw JSON from the admin UI
Replies as comments — incoming Fediverse replies to local nodes are optionally saved as Backdrop comments
Comment moderation — Fediverse replies can be held for approval before publishing
Likes and boosts — incoming Like and Announce activities are counted and displayed on nodes
HTTP Signatures — all outgoing requests are signed; all incoming requests are verified (draft-cavage)
Blocklist — block specific actors by URI or entire domains; blocked followers are also removed
Fediverse handle support — blocklist accepts @user@domain handles in addition to raw actor URIs
Rate limiting — per-actor inbox rate limiting with configurable window and request limit
Subscribe page — a form at /fediverse/subscribe lets visitors initiate a remote follow from their own instance
RSA keypair — a 2048-bit keypair is generated on install and stored in the database
Views integration — the followers table is exposed to the Views module for building custom displays

Configuration

All settings are at Administration › Configuration › Web services › Backdrop Federation (admin/config/services/fediverse).

Tab	Purpose
Settings	Enable/disable federation, actor username, display name, bio, content types, reply handling
Followers	List of current Fediverse followers
Outbox	Browse outgoing activities and inspect raw JSON (debug)
Blocklist	Block actors or domains; accepts raw URIs or `@user@domain` handles
Rate Limit	Max requests per actor per time window

How It Works

See Technical_information.md for a detailed breakdown of each subsystem: actor discovery, content federation, delivery, inbox handling, HTTP signatures, blocklist, and rate limiting.

Sub-module: Backdrop Federation Follow

The Backdrop Federation Follow sub-module adds two-way federation: the site can follow remote Fediverse accounts and receive their posts into a local feed.

Features

Follow any Fediverse account by entering a @user@domain handle in the admin UI
Resolves handles via WebFinger and sends a signed Follow activity automatically
Tracks follow status (Pending, Accepted, Rejected) as remote servers respond
Stores incoming posts from followed accounts in a local feed
Feed posts are updated or removed when the remote account edits or deletes them
Unfollow sends a signed Undo Follow activity and removes the account's posts from the local feed
Pause / Resume — pause a followed account to temporarily stop receiving their posts without losing the record; resume re-sends a Follow and resumes delivery
Boosts — optionally include boosted posts in the local feed (configurable globally)
Feed block — a "Fediverse Following Feed" block for placement in Backdrop layouts
Views integration — both the feed posts and followed accounts tables are exposed to the Views module for building custom displays, including public-facing feed pages

Configuration

Two additional tabs appear at admin/config/services/fediverse when the sub-module is enabled:

Tab	Purpose
Following	Manage followed accounts; follow, pause, resume, or unfollow
Feed	Browse posts received from followed accounts (paginated)

Feed settings (retention period, boost inclusion) are on the Following tab.

Fediverse Following Feed Block

A Fediverse Following Feed block is available for placement in any Backdrop layout region. Each block instance has its own settings:

Setting	Description
Number of posts	How many recent posts to display (5, 10, 15, 20, 25, or 50)
Show avatars	Display the poster's avatar next to each post
Truncate content	Optionally truncate post text (no limit, 140, 280, or 500 characters)
Max image width / height	Cap the size of inline images (100–400 px)

Content is sanitized with filter_xss at ingest time and output directly in the block
Hashtag links are converted to plain text; regular hyperlinks are preserved
Boosts show the booster's name and avatar alongside the original post
A "View all posts" link at the bottom of the block links to the admin feed page

How It Works

Admin enters a handle at the Following tab
The module resolves the handle via WebFinger to get the actor URI and inbox
A signed Follow activity is POSTed to the remote inbox
The remote server sends Accept or Reject back to /fediverse/inbox
On Accept, the follow status is updated and the remote server begins delivering posts
Incoming Create activities from followed accounts are stored in backdrop_federation_feed
Update and Delete activities from followed accounts update or remove the stored posts
Announce (boost) activities optionally add the boosted post to the feed; Undo Announce removes it

Developer Hook

The parent module invokes hook_backdrop_federation_inbox_activity($activity) for every verified incoming activity. The Follow sub-module uses this to handle Accept, Reject, Create, Update, Delete, Announce, and Undo activities from followed accounts without modifying the parent module's inbox handler. Other modules can implement this hook to react to any incoming ActivityPub activity.

Database Tables

Core module

Table	Purpose
`backdrop_federation_keypair`	RSA keypair for signing
`backdrop_federation_followers`	Remote followers and their inbox URIs
`backdrop_federation_outbox`	Outgoing activities
`backdrop_federation_received`	Incoming objects mapped to comment IDs
`backdrop_federation_reactions`	Like and Announce counts per node
`backdrop_federation_blocklist`	Blocked actors and domains
`backdrop_federation_rate_limit`	Per-actor request counts for rate limiting