activitypub / includes / rest / class-server.php

class-server.php in ActivityPub 9.2.0, at includes/rest/class-server.php

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1	<?php
2	/**
3	* Server REST-Class file.
4	*
5	* @package Activitypub
6	*/
7
8	namespace Activitypub\Rest;
9
10	use Activitypub\Signature;
11
12	use function Activitypub\maybe_set_no_store;
13	use function Activitypub\use_authorized_fetch;
14
15	/**
16	* ActivityPub Server REST-Class.
17	*
18	* @author Django Doucet
19	*
20	* @see https://www.w3.org/TR/activitypub/#security-verification
21	*/
22	class Server {
23	/**
24	* Initialize the class, registering WordPress hooks.
25	*/
26	public static function init() {
27	\add_filter( 'rest_pre_dispatch', array( self::class, 'maybe_add_actor_from_signature' ), 10, 3 );
28	\add_filter( 'rest_request_before_callbacks', array( self::class, 'validate_requests' ), 9, 3 );
29	\add_filter( 'rest_request_parameter_order', array( self::class, 'request_parameter_order' ), 10, 2 );
30
31	\add_filter( 'rest_post_dispatch', array( self::class, 'filter_output' ), 10, 3 );
32	\add_filter( 'rest_post_dispatch', array( self::class, 'add_cache_headers' ), 10, 3 );
33	\add_filter( 'rest_post_dispatch', array( self::class, 'add_cors_headers' ), 10, 3 );
34	\add_filter( 'rest_allowed_cors_headers', array( self::class, 'allow_cors_headers' ), 10, 2 );
35	}
36
37	/**
38	* Callback function to validate incoming ActivityPub requests
39	*
40	* @param \WP_REST_Response\|\WP_HTTP_Response\|\WP_Error\|mixed $response Result to send to the client.
41	* Usually a WP_REST_Response or WP_Error.
42	* @param array $handler Route handler used for the request.
43	* @param \WP_REST_Request $request Request used to generate the response.
44	*
45	* @return mixed\|\WP_Error The response, error, or modified response.
46	*/
47	public static function validate_requests( $response, $handler, $request ) {
48	if ( 'HEAD' === $request->get_method() ) {
49	return $response;
50	}
51
52	$route = $request->get_route();
53
54	if (
55	\is_wp_error( $response ) \|\|
56	! \str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE )
57	) {
58	return $response;
59	}
60
61	$params = $request->get_json_params();
62
63	// Type is required for ActivityPub requests, so it fail later in the process.
64	if ( ! isset( $params['type'] ) ) {
65	return $response;
66	}
67
68	if (
69	ACTIVITYPUB_DISABLE_INCOMING_INTERACTIONS &&
70	\in_array( $params['type'], array( 'Create', 'Like', 'Announce' ), true )
71	) {
72	return new \WP_Error(
73	'activitypub_server_does_not_accept_incoming_interactions',
74	\__( 'This server does not accept incoming interactions.', 'activitypub' ),
75	// We have to use a 2XX status code here, because otherwise the response will be
76	// treated as an error and Mastodon might block this WordPress instance.
77	array( 'status' => 202 )
78	);
79	}
80
81	return $response;
82	}
83
84	/**
85	* Modify the parameter priority order for a REST API request.
86	*
87	* @param string[] $order Array of types to check, in order of priority.
88	* @param \WP_REST_Request $request The request object.
89	*
90	* @return string[] The modified order of types to check.
91	*/
92	public static function request_parameter_order( $order, $request ) {
93	$route = $request->get_route();
94
95	// Check if it is an activitypub request and exclude webfinger and nodeinfo endpoints.
96	if ( ! \str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE ) ) {
97	return $order;
98	}
99
100	$method = $request->get_method();
101
102	if ( \WP_REST_Server::CREATABLE !== $method ) {
103	return $order;
104	}
105
106	return array(
107	'JSON',
108	'POST',
109	'URL',
110	'defaults',
111	);
112	}
113
114	/**
115	* Backfill a missing `actor` on incoming FeatureRequest activities from the signature.
116	*
117	* Mastodon (FEP-7aa9) omits `actor` from the FeatureRequest body and conveys the
118	* requesting actor only through the HTTP signature keyId. Our inbox routes require
119	* `actor`, so such a request is rejected during parameter validation before it can
120	* reach the inbox or its handler, which is why no Accept is ever sent.
121	*
122	* Derive the actor from the keyId and add it as a request parameter. The actor is
123	* injected with `set_param()` rather than by rewriting the request body, so the raw
124	* body stays byte-identical and the signed `Digest` still verifies. Inbox POSTs read
125	* JSON parameters first (see `request_parameter_order()`), so the value is visible to
126	* both parameter validation and the handler via `get_json_params()`.
127	*
128	* Scoped to FeatureRequest, the only activity type known to address this way. Runs on
129	* `rest_pre_dispatch` because that is the only hook that fires before required-parameter
130	* validation. Signature verification still runs afterwards and remains authoritative:
131	* the injected actor is derived from the very keyId the signature is checked against, so
132	* it cannot be used to impersonate another actor.
133	*
134	* @since 9.0.0
135	*
136	* @param mixed $result Response to replace the request with, or null to continue.
137	* @param \WP_REST_Server $server Server instance.
138	* @param \WP_REST_Request $request The request object.
139	*
140	* @return mixed The unmodified `$result`.
141	*/
142	public static function maybe_add_actor_from_signature( $result, $server, $request ) {
143	// Respect an earlier short-circuit.
144	if ( null !== $result ) {
145	return $result;
146	}
147
148	if ( \WP_REST_Server::CREATABLE !== $request->get_method() ) {
149	return $result;
150	}
151
152	$route = $request->get_route();
153	if (
154	! \str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE ) \|\|
155	! \str_ends_with( $route, '/inbox' )
156	) {
157	return $result;
158	}
159
160	$json = $request->get_json_params();
161	if ( ! \is_array( $json ) \|\| 'FeatureRequest' !== ( $json['type'] ?? '' ) \|\| ! empty( $json['actor'] ) ) {
162	return $result;
163	}
164
165	$key_id = Signature::get_key_id( $request );
166	if ( ! $key_id ) {
167	return $result;
168	}
169
170	$request->set_param( 'actor', \strip_fragment_from_url( $key_id ) );
171
172	return $result;
173	}
174
175	/**
176	* Filters the REST API response to properly handle the ActivityPub error formatting.
177	*
178	* @see https://codeberg.org/fediverse/fep/src/branch/main/fep/c180/fep-c180.md
179	*
180	* @param \WP_HTTP_Response $response Result to send to the client. Usually a `WP_REST_Response`.
181	* @param \WP_REST_Server $server Server instance.
182	* @param \WP_REST_Request $request Request used to generate the response.
183	*
184	* @return \WP_HTTP_Response The filtered response.
185	*/
186	public static function filter_output( $response, $server, $request ) {
187	$route = $request->get_route();
188
189	// Check if it is an activitypub request and exclude webfinger and nodeinfo endpoints.
190	if ( ! \str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE ) ) {
191	return $response;
192	}
193
194	// Exclude OAuth endpoints - they have their own error format per RFC 6749.
195	if ( \str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE . '/oauth' ) ) {
196	return $response;
197	}
198
199	// Only alter responses that return an error status code.
200	if ( $response->get_status() < 400 ) {
201	return $response;
202	}
203
204	$data = $response->get_data();
205
206	// Ensure that `$data` was already converted to a response.
207	if ( \is_wp_error( $data ) ) {
208	$response = \rest_convert_error_to_response( $data );
209	$data = $response->get_data();
210	}
211
212	$error = array(
213	'type' => 'about:blank',
214	'title' => $data['code'] ?? '',
215	'detail' => $data['message'] ?? '',
216	'status' => $response->get_status(),
217
218	/*
219	* Provides the unstructured error data.
220	*
221	* @see https://nodeinfo.diaspora.software/schema.html#metadata.
222	*/
223	'metadata' => $data,
224	);
225
226	$response->set_data( $error );
227
228	return $response;
229	}
230
231	/**
232	* Add cache headers to ActivityPub responses.
233	*
234	* Responses on these routes are not the same for every caller: Authorized Fetch
235	* varies them by signing key, and the ActivityPub API varies them by access token.
236	* Shared caches are told to key on those headers, and a response produced for a
237	* caller that presented credentials is marked as belonging to that caller alone.
238	*
239	* @since 9.2.0
240	*
241	* @param \WP_REST_Response $response Result to send to the client.
242	* @param \WP_REST_Server $server Server instance.
243	* @param \WP_REST_Request $request Request used to generate the response.
244	*
245	* @return \WP_REST_Response The response object.
246	*/
247	public static function add_cache_headers( $response, $server, $request ) {
248	if ( ! \str_starts_with( $request->get_route(), '/' . ACTIVITYPUB_REST_NAMESPACE ) ) {
249	return $response;
250	}
251
252	/*
253	* A request authenticated by WP session can get a personalized response even on a route whose
254	* permission callback is `__return_true`: `/interactions` redirects by the current user, and
255	* verify_owner() surfaces private items in otherwise public collections. The session cookie is
256	* not part of Vary, so mark any logged-in response private before the public shortcut below.
257	*/
258	if ( \is_user_logged_in() ) {
259	maybe_set_no_store( $response );
260
261	return $response;
262	}
263
264	/*
265	* A route that authorizes every caller identically (permission_callback `__return_true`) returns
266	* a public response, even under Authorized Fetch, where Mastodon still signs its GETs. Leave it
267	* without caller-varying cache directives so public collections such as thread replies and
268	* context stay cacheable at the edge. Routes that gate on the caller fall through below.
269	*/
270	$attributes = $request->get_attributes();
271	if ( isset( $attributes['permission_callback'] ) && '__return_true' === $attributes['permission_callback'] ) {
272	return $response;
273	}
274
275	$authorized_fetch = use_authorized_fetch();
276
277	/*
278	* Authorization always affects the response: the ActivityPub API varies it by access token.
279	* The HTTP-signature headers only affect it under Authorized Fetch; with it off the response
280	* is identical for every caller, and Mastodon sends a fresh Signature-Input on each GET, so
281	* varying on them would mint a unique cache variant per request and defeat shared caching.
282	*/
283	$vary = array( 'Authorization' );
284
285	if ( $authorized_fetch ) {
286	$vary[] = 'Signature';
287	$vary[] = 'Signature-Input';
288	}
289
290	// Appended, so the CORS handler's own `Vary: Origin` survives.
291	$response->header( 'Vary', \implode( ', ', $vary ), false );
292
293	/*
294	* Only mark a credentialed response private when Authorized Fetch actually varies it. With
295	* Authorized Fetch off, a signed request gets the same public response as everyone else
296	* (Mastodon signs its GETs by default), so `no-store` would needlessly drop it from every
297	* CDN. The `Vary: Authorization` above still keeps a token-credentialed response from being reused.
298	*/
299	if ( $authorized_fetch ) {
300	$credentials = array( 'authorization', 'signature', 'signature-input' );
301
302	foreach ( $credentials as $header ) {
303	if ( $request->get_header( $header ) ) {
304	maybe_set_no_store( $response );
305	break;
306	}
307	}
308	}
309
310	return $response;
311	}
312
313	/**
314	* Add CORS headers to ActivityPub REST responses.
315	*
316	* @param \WP_REST_Response $response The REST response.
317	* @param \WP_REST_Server $server The REST server instance.
318	* @param \WP_REST_Request $request The request object.
319	*
320	* @return \WP_REST_Response The modified response.
321	*/
322	public static function add_cors_headers( $response, $server, $request ) {
323	$route = $request->get_route();
324	$namespace = '/' . ACTIVITYPUB_REST_NAMESPACE;
325
326	// Only add CORS to ActivityPub endpoints, except the interactive OAuth authorize endpoint.
327	if ( ! \str_starts_with( $route, $namespace ) \|\| \str_starts_with( $route, $namespace . '/oauth/authorize' ) ) {
328	return $response;
329	}
330
331	/*
332	* ActivityPub data is meant to be publicly readable by federation peers
333	* and browser-side clients. We do not enable credentialed cross-origin
334	* access: cookie auth would still be rejected by WordPress core's
335	* REST nonce check, and OAuth Bearer tokens travel in the
336	* Authorization header — which is permitted via Allow-Headers and
337	* does not require Allow-Credentials.
338	*
339	* Allow-Headers is contributed by core (which already lists `X-WP-Nonce`,
340	* `Authorization`, `Content-Type`, `Content-Disposition`, and `Content-MD5`)
341	* and extended for ActivityPub via the `rest_allowed_cors_headers` filter
342	* in self::allow_cors_headers().
343	*/
344	$response->header( 'Access-Control-Allow-Origin', '*' );
345	$response->header( 'Access-Control-Allow-Methods', 'GET, POST, OPTIONS' );
346
347	return $response;
348	}
349
350	/**
351	* Extend the CORS Allow-Headers list for ActivityPub REST endpoints.
352	*
353	* Adds the headers ActivityPub clients need on top of WordPress core's
354	* defaults: `Accept` for content negotiation and `Last-Event-ID` for
355	* Server-Sent Events resume.
356	*
357	* @since 8.3.0
358	*
359	* @param string[] $allow_headers Headers core currently permits in CORS requests.
360	* @param \WP_REST_Request $request The current REST request.
361	*
362	* @return string[] The (possibly extended) list of allowed headers.
363	*/
364	public static function allow_cors_headers( $allow_headers, $request ) {
365	$route = $request->get_route();
366	$namespace = '/' . ACTIVITYPUB_REST_NAMESPACE;
367
368	if ( ! \str_starts_with( $route, $namespace ) \|\| \str_starts_with( $route, $namespace . '/oauth/authorize' ) ) {
369	return $allow_headers;
370	}
371
372	return \array_values( \array_unique( \array_merge( (array) $allow_headers, array( 'Accept', 'Last-Event-ID' ) ) ) );
373	}
374
375	/**
376	* Send CORS headers directly via header().
377	*
378	* Use this for endpoints that bypass the REST response flow
379	* (e.g. SSE streams that call exit() instead of returning a WP_REST_Response).
380	*
381	* @since 8.1.0
382	*/
383	public static function send_cors_headers() {
384	\header( 'Access-Control-Allow-Origin: *' );
385	\header( 'Access-Control-Allow-Methods: GET, POST, OPTIONS' );
386	\header( 'Access-Control-Allow-Headers: Authorization, X-WP-Nonce, Content-Disposition, Content-MD5, Content-Type, Accept, Last-Event-ID' );
387	}
388	}
389