Merge pull request #299 from mediaformat/signature_verification

Signature verification

activitypub.php

@@ -27,6 +27,7 @@ function init() {
 	\defined( 'ACTIVITYPUB_HASHTAGS_REGEXP' ) || \define( 'ACTIVITYPUB_HASHTAGS_REGEXP', '(?:(?<=\s)|(?<=<p>)|(?<=<br>)|^)#([A-Za-z0-9_]+)(?:(?=\s|[[:punct:]]|$))' );
 	\defined( 'ACTIVITYPUB_USERNAME_REGEXP' ) || \define( 'ACTIVITYPUB_USERNAME_REGEXP', '(?:([A-Za-z0-9_-]+)@((?:[A-Za-z0-9_-]+\.)+[A-Za-z]+))' );
 	\defined( 'ACTIVITYPUB_CUSTOM_POST_CONTENT' ) || \define( 'ACTIVITYPUB_CUSTOM_POST_CONTENT', "<strong>[ap_title]</strong>\n\n[ap_content]\n\n[ap_hashtags]\n\n[ap_shortlink]" );
+	\defined( 'ACTIVITYPUB_SECURE_MODE' ) || \define( 'ACTIVITYPUB_SECURE_MODE', apply_filters( 'activitypub_secure_mode', $value = false ) );
 
 	\define( 'ACTIVITYPUB_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 	\define( 'ACTIVITYPUB_PLUGIN_BASENAME', plugin_basename( __FILE__ ) );
@@ -43,6 +44,7 @@ function init() {
 	Rest\Followers::init();
 	Rest\Following::init();
 	Rest\Webfinger::init();
+	Rest\Server::init();
 
 	Admin::init();
 	Hashtag::init();

includes/class-activitypub.php

@@ -1,6 +1,8 @@
 <?php
 namespace Activitypub;
 
+use Activitypub\Signature;
+
 /**
  * ActivityPub Class
  *
@@ -87,34 +89,14 @@ class Activitypub {
 			$json_template = ACTIVITYPUB_PLUGIN_DIR . '/templates/blog-json.php';
 		}
 
-		global $wp_query;
+		if ( is_activitypub_request() ) {
-
+			if ( ACTIVITYPUB_SECURE_MODE ) {
-		if ( isset( $wp_query->query_vars['activitypub'] ) ) {
+				$verification = Signature::verify_http_signature( $_SERVER );
-			return $json_template;
+				if ( \is_wp_error( $verification ) ) {
-		}
+					// fallback as template_loader can't return http headers
-
+					return $template;
-		if ( ! isset( $_SERVER['HTTP_ACCEPT'] ) ) {
+				}
-			return $template;
+			}
-		}
-
-		$accept_header = $_SERVER['HTTP_ACCEPT'];
-
-		if (
-			\stristr( $accept_header, 'application/activity+json' ) ||
-			\stristr( $accept_header, 'application/ld+json' )
-		) {
-			return $json_template;
-		}
-
-		// Accept header as an array.
-		$accept = \explode( ',', \trim( $accept_header ) );
-
-		if (
-			\in_array( 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"', $accept, true ) ||
-			\in_array( 'application/activity+json', $accept, true ) ||
-			\in_array( 'application/ld+json', $accept, true ) ||
-			\in_array( 'application/json', $accept, true )
-		) {
 			return $json_template;
 		}
 

includes/class-http.php

@@ -2,6 +2,7 @@
 namespace Activitypub;
 
 use WP_Error;
+use Activitypub\Model\User;
 
 /**
  * ActivityPub HTTP Class
@@ -33,7 +34,7 @@ class Http {
 			'headers' => array(
 				'Accept' => 'application/activity+json',
 				'Content-Type' => 'application/activity+json',
-				'Digest' => "SHA-256=$digest",
+				'Digest' => $digest,
 				'Signature' => $signature,
 				'Date' => $date,
 			),
@@ -60,9 +61,9 @@ class Http {
 	 *
 	 * @return array|WP_Error The GET Response or an WP_ERROR
 	 */
-	public static function get( $url, $user_id ) {
+	public static function get( $url ) {
 		$date = \gmdate( 'D, d M Y H:i:s T' );
-		$signature = Signature::generate_signature( $user_id, 'get', $url, $date );
+		$signature = Signature::generate_signature( User::APPLICATION_USER_ID, 'get', $url, $date );
 
 		$wp_version = \get_bloginfo( 'version' );
 		$user_agent = \apply_filters( 'http_headers_useragent', 'WordPress/' . $wp_version . '; ' . \get_bloginfo( 'url' ) );
@@ -86,7 +87,7 @@ class Http {
 			$response = new WP_Error( $code, __( 'Failed HTTP Request', 'activitypub' ) );
 		}
 
-		\do_action( 'activitypub_safe_remote_get_response', $response, $url, $user_id );
+		\do_action( 'activitypub_safe_remote_get_response', $response, $url );
 
 		return $response;
 	}

includes/class-signature.php

@@ -1,53 +1,77 @@
 <?php
 namespace Activitypub;
 
+use WP_Error;
+use DateTime;
+use DateTimeZone;
+use Activitypub\Model\User;
+
 /**
  * ActivityPub Signature Class
  *
  * @author Matthias Pfefferle
+ * @author Django Doucet
  */
 class Signature {
 
 	/**
-	 * @param int $user_id
+	 * Return the public key for a given user.
 	 *
-	 * @return mixed
+	 * @param int  $user_id The WordPress User ID.
+	 * @param bool $force   Force the generation of a new key pair.
+	 *
+	 * @return mixed The public key.
 	 */
 	public static function get_public_key( $user_id, $force = false ) {
-		$key = \get_user_meta( $user_id, 'magic_sig_public_key' );
+		if ( $force ) {
-
+			self::generate_key_pair( $user_id );
-		if ( $key && ! $force ) {
-			return $key[0];
 		}
 
-		self::generate_key_pair( $user_id );
+		if ( User::APPLICATION_USER_ID === $user_id ) {
-		$key = \get_user_meta( $user_id, 'magic_sig_public_key' );
+			$key = \get_option( 'activitypub_magic_sig_public_key' );
+		} else {
+			$key = \get_user_meta( $user_id, 'magic_sig_public_key', true );
+		}
 
-		return $key[0];
+		if ( ! $key ) {
+			return self::get_public_key( $user_id, true );
+		}
+
+		return $key;
 	}
 
 	/**
-	 * @param int $user_id
+	 * Return the private key for a given user.
 	 *
-	 * @return mixed
+	 * @param int  $user_id The WordPress User ID.
+	 * @param bool $force   Force the generation of a new key pair.
+	 *
+	 * @return mixed The private key.
 	 */
 	public static function get_private_key( $user_id, $force = false ) {
-		$key = \get_user_meta( $user_id, 'magic_sig_private_key' );
+		if ( $force ) {
-
+			self::generate_key_pair( $user_id );
-		if ( $key && ! $force ) {
-			return $key[0];
 		}
 
-		self::generate_key_pair( $user_id );
+		if ( User::APPLICATION_USER_ID === $user_id ) {
-		$key = \get_user_meta( $user_id, 'magic_sig_private_key' );
+			$key = \get_option( 'activitypub_magic_sig_private_key' );
+		} else {
+			$key = \get_user_meta( $user_id, 'magic_sig_private_key', true );
+		}
 
-		return $key[0];
+		if ( ! $key ) {
+			return self::get_private_key( $user_id, true );
+		}
+
+		return $key;
 	}
 
 	/**
 	 * Generates the pair keys
 	 *
-	 * @param int $user_id
+	 * @param int $user_id The WordPress User ID.
+	 *
+	 * @return void
 	 */
 	public static function generate_key_pair( $user_id ) {
 		$config = array(
@@ -60,16 +84,35 @@ class Signature {
 		$priv_key = null;
 
 		\openssl_pkey_export( $key, $priv_key );
-
-		// private key
-		\update_user_meta( $user_id, 'magic_sig_private_key', $priv_key );
-
 		$detail = \openssl_pkey_get_details( $key );
 
-		// public key
+		if ( User::APPLICATION_USER_ID === $user_id ) {
-		\update_user_meta( $user_id, 'magic_sig_public_key', $detail['key'] );
+			// private key
+			\update_option( 'activitypub_magic_sig_private_key', $priv_key );
+
+			// public key
+			\update_option( 'activitypub_magic_sig_public_key', $detail['key'] );
+
+		} else {
+			// private key
+			\update_user_meta( $user_id, 'magic_sig_private_key', $priv_key );
+
+			// public key
+			\update_user_meta( $user_id, 'magic_sig_public_key', $detail['key'] );
+		}
 	}
 
+	/**
+	 * Generates the Signature for a HTTP Request
+	 *
+	 * @param int    $user_id     The WordPress User ID.
+	 * @param string $http_method The HTTP method.
+	 * @param string $url         The URL to send the request to.
+	 * @param string $date        The date the request is sent.
+	 * @param string $digest      The digest of the request body.
+	 *
+	 * @return string The signature.
+	 */
 	public static function generate_signature( $user_id, $http_method, $url, $date, $digest = null ) {
 		$key = self::get_private_key( $user_id );
 
@@ -88,8 +131,10 @@ class Signature {
 			$path .= '?' . $url_parts['query'];
 		}
 
+		$http_method = \strtolower( $http_method );
+
 		if ( ! empty( $digest ) ) {
-			$signed_string = "(request-target): $http_method $path\nhost: $host\ndate: $date\ndigest: SHA-256=$digest";
+			$signed_string = "(request-target): $http_method $path\nhost: $host\ndate: $date\ndigest: $digest";
 		} else {
 			$signed_string = "(request-target): $http_method $path\nhost: $host\ndate: $date";
 		}
@@ -98,7 +143,11 @@ class Signature {
 		\openssl_sign( $signed_string, $signature, $key, \OPENSSL_ALGO_SHA256 );
 		$signature = \base64_encode( $signature ); // phpcs:ignore
 
-		$key_id = \get_author_posts_url( $user_id ) . '#main-key';
+		if ( User::APPLICATION_USER_ID === $user_id ) {
+			$key_id = \get_rest_url( null, 'activitypub/1.0/application#main-key' );
+		} else {
+			$key_id = \get_author_posts_url( $user_id ) . '#main-key';
+		}
 
 		if ( ! empty( $digest ) ) {
 			return \sprintf( 'keyId="%s",algorithm="rsa-sha256",headers="(request-target) host date digest",signature="%s"', $key_id, $signature );
@@ -107,12 +156,262 @@ class Signature {
 		}
 	}
 
-	public static function verify_signature( $headers, $signature ) {
+	/**
+	 * Verifies the http signatures
+	 *
+	 * @param WP_REQUEST|array $request The request object or $_SERVER array.
+	 *
+	 * @return mixed A boolean or WP_Error.
+	 */
+	public static function verify_http_signature( $request ) {
+		if ( is_object( $request ) ) { // REST Request object
+			// check if route starts with "index.php"
+			if ( str_starts_with( $request->get_route(), '/index.php' ) ) {
+				$route = $request->get_route();
+			} else {
+				$route = '/' . rest_get_url_prefix() . '/' . ltrim( $request->get_route(), '/' );
+			}
+			$headers = $request->get_headers();
+			$actor = isset( json_decode( $request->get_body() )->actor ) ? json_decode( $request->get_body() )->actor : '';
+			$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' ' . $route;
+		} else {
+			$request = self::format_server_request( $request );
+			$headers = $request['headers']; // $_SERVER array
+			$actor = null;
+			$headers['(request-target)'][0] = strtolower( $headers['request_method'][0] ) . ' ' . $headers['request_uri'][0];
+		}
 
+		if ( ! isset( $headers['signature'] ) ) {
+			return new WP_Error( 'activitypub_signature', 'Request not signed', array( 'status' => 403 ) );
+		}
+
+		if ( array_key_exists( 'signature', $headers ) ) {
+			$signature_block = self::parse_signature_header( $headers['signature'] );
+		} elseif ( array_key_exists( 'authorization', $headers ) ) {
+			$signature_block = self::parse_signature_header( $headers['authorization'] );
+		}
+
+		if ( ! isset( $signature_block ) || ! $signature_block ) {
+			return new WP_Error( 'activitypub_signature', 'Incompatible request signature. keyId and signature are required', array( 'status' => 403 ) );
+		}
+
+		$signed_headers = $signature_block['headers'];
+		if ( ! $signed_headers ) {
+			$signed_headers = array( 'date' );
+		}
+
+		$signed_data = self::get_signed_data( $signed_headers, $signature_block, $headers );
+		if ( ! $signed_data ) {
+			return new WP_Error( 'activitypub_signature', 'Signed request date outside acceptable time window', array( 'status' => 403 ) );
+		}
+
+		$algorithm = self::get_signature_algorithm( $signature_block );
+		if ( ! $algorithm ) {
+			return new WP_Error( 'activitypub_signature', 'Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)', array( 'status' => 403 ) );
+		}
+
+		if ( \in_array( 'digest', $signed_headers, true ) && isset( $body ) ) {
+			if ( is_array( $headers['digest'] ) ) {
+				$headers['digest'] = $headers['digest'][0];
+			}
+			$digest = explode( '=', $headers['digest'], 2 );
+			if ( 'SHA-256' === $digest[0] ) {
+				$hashalg = 'sha256';
+			}
+			if ( 'SHA-512' === $digest[0] ) {
+				$hashalg = 'sha512';
+			}
+
+			if ( \base64_encode( \hash( $hashalg, $body, true ) ) !== $digest[1] ) { // phpcs:ignore
+				return new WP_Error( 'activitypub_signature', 'Invalid Digest header', array( 'status' => 403 ) );
+			}
+		}
+
+		if ( $actor ) {
+			$public_key = self::get_remote_key( $actor );
+		} else {
+			$public_key = self::get_remote_key( $signature_block['keyId'] );
+		}
+		if ( \is_wp_error( $public_key ) ) {
+			return $public_key;
+		}
+
+		$verified = \openssl_verify( $signed_data, $signature_block['signature'], $public_key, $algorithm ) > 0;
+
+		if ( ! $verified ) {
+			return new WP_Error( 'activitypub_signature', 'Invalid signature', array( 'status' => 403 ) );
+		}
+		return $verified;
 	}
 
+	/**
+	 * Get public key from key_id
+	 *
+	 * @param string $key_id The URL to the public key.
+	 *
+	 * @return string The public key.
+	 */
+	public static function get_remote_key( $key_id ) { // phpcs:ignore
+		$actor = \Activitypub\get_remote_metadata_by_actor( strtok( strip_fragment_from_url( $key_id ), '?' ) ); // phpcs:ignore
+		if ( \is_wp_error( $actor ) ) {
+			return $actor;
+		}
+		if ( isset( $actor['publicKey']['publicKeyPem'] ) ) {
+			return \rtrim( $actor['publicKey']['publicKeyPem'] ); // phpcs:ignore
+		}
+		return null;
+	}
+
+	/**
+	 * Gets the signature algorithm from the signature header
+	 *
+	 * @param array $signature_block
+	 *
+	 * @return string The signature algorithm.
+	 */
+	public static function get_signature_algorithm( $signature_block ) {
+		if ( $signature_block['algorithm'] ) {
+			switch ( $signature_block['algorithm'] ) {
+				case 'rsa-sha-512':
+					return 'sha512'; //hs2019 https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12
+				default:
+					return 'sha256';
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * Parses the Signature header
+	 *
+	 * @param array $header The signature header.
+	 *
+	 * @return array signature parts
+	 */
+	public static function parse_signature_header( $header ) {
+		$parsed_header = array();
+		$matches       = array();
+		$h_string      = \implode( ',', (array) $header[0] );
+
+		if ( \preg_match( '/keyId="(.*?)"/ism', $h_string, $matches ) ) {
+			$parsed_header['keyId'] = $matches[1];
+		}
+		if ( \preg_match( '/created=([0-9]*)/ism', $h_string, $matches ) ) {
+			$parsed_header['(created)'] = $matches[1];
+		}
+		if ( \preg_match( '/expires=([0-9]*)/ism', $h_string, $matches ) ) {
+			$parsed_header['(expires)'] = $matches[1];
+		}
+		if ( \preg_match( '/algorithm="(.*?)"/ism', $h_string, $matches ) ) {
+			$parsed_header['algorithm'] = $matches[1];
+		}
+		if ( \preg_match( '/headers="(.*?)"/ism', $h_string, $matches ) ) {
+			$parsed_header['headers'] = \explode( ' ', $matches[1] );
+		}
+		if ( \preg_match( '/signature="(.*?)"/ism', $h_string, $matches ) ) {
+			$parsed_header['signature'] = \base64_decode( preg_replace( '/\s+/', '', $matches[1] ) ); // phpcs:ignore
+		}
+
+		if ( ( $parsed_header['signature'] ) && ( $parsed_header['algorithm'] ) && ( ! $parsed_header['headers'] ) ) {
+			$parsed_header['headers'] = array( 'date' );
+		}
+
+		return $parsed_header;
+	}
+
+	/**
+	 * Gets the header data from the included pseudo headers
+	 *
+	 * @param array $signed_headers
+	 * @param array $signature_block (pseudo-headers)
+	 * @param array $headers         (http headers)
+	 *
+	 * @return string signed headers for comparison
+	 */
+	public static function get_signed_data( $signed_headers, $signature_block, $headers ) {
+		$signed_data = '';
+		// This also verifies time-based values by returning false if any of these are out of range.
+		foreach ( $signed_headers as $header ) {
+			if ( 'host' === $header ) {
+				if ( isset( $headers['x_original_host'] ) ) {
+					$signed_data .= $header . ': ' . $headers['x_original_host'][0] . "\n";
+					continue;
+				}
+			}
+			if ( '(request-target)' === $header ) {
+				$signed_data .= $header . ': ' . $headers[ $header ][0] . "\n";
+				continue;
+			}
+			if ( str_contains( $header, '-' ) ) {
+				$signed_data .= $header . ': ' . $headers[ str_replace( '-', '_', $header ) ][0] . "\n";
+				continue;
+			}
+			if ( '(created)' === $header ) {
+				if ( ! empty( $signature_block['(created)'] ) && \intval( $signature_block['(created)'] ) > \time() ) {
+					// created in future
+					return false;
+				}
+			}
+			if ( '(expires)' === $header ) {
+				if ( ! empty( $signature_block['(expires)'] ) && \intval( $signature_block['(expires)'] ) < \time() ) {
+					// expired in past
+					return false;
+				}
+			}
+			if ( 'date' === $header ) {
+				// allow a bit of leeway for misconfigured clocks.
+				$d = new DateTime( $headers[ $header ][0] );
+				$d->setTimeZone( new DateTimeZone( 'UTC' ) );
+				$c = $d->format( 'U' );
+
+				$dplus = time() + ( 3 * HOUR_IN_SECONDS );
+				$dminus = time() - ( 3 * HOUR_IN_SECONDS );
+
+				if ( $c > $dplus || $c < $dminus ) {
+					// time out of range
+					return false;
+				}
+			}
+			$signed_data .= $header . ': ' . $headers[ $header ][0] . "\n";
+		}
+		return \rtrim( $signed_data, "\n" );
+	}
+
+	/**
+	 * Generates the digest for a HTTP Request
+	 *
+	 * @param string $body The body of the request.
+	 *
+	 * @return string The digest.
+	 */
 	public static function generate_digest( $body ) {
 		$digest = \base64_encode( \hash( 'sha256', $body, true ) ); // phpcs:ignore
-		return "$digest";
+		return "SHA-256=$digest";
+	}
+
+	/**
+	 * Formats the $_SERVER to resemble the WP_REST_REQUEST array,
+	 * for use with verify_http_signature()
+	 *
+	 * @param array $_SERVER The $_SERVER array.
+	 *
+	 * @return array $request The formatted request array.
+	 */
+	public static function format_server_request( $server ) {
+		$request = array();
+		foreach ( $server as $param_key => $param_val ) {
+			$req_param = strtolower( $param_key );
+			if ( 'REQUEST_URI' === $req_param ) {
+				$request['headers']['route'][] = $param_val;
+			} else {
+				$header_key = str_replace(
+					'http_',
+					'',
+					$req_param
+				);
+				$request['headers'][ $header_key ][] = \wp_unslash( $param_val );
+			}
+		}
+		return $request;
 	}
 }

includes/functions.php

@@ -36,8 +36,8 @@ function safe_remote_post( $url, $body, $user_id ) {
 	return \Activitypub\Http::post( $url, $body, $user_id );
 }
 
-function safe_remote_get( $url, $user_id ) {
+function safe_remote_get( $url ) {
-	return \Activitypub\Http::get( $url, $user_id );
+	return \Activitypub\Http::get( $url );
 }
 
 /**
@@ -92,21 +92,11 @@ function get_remote_metadata_by_actor( $actor, $cached = true ) {
 		return $metadata;
 	}
 
-	$user = \get_users(
-		array(
-			'number' => 1,
-			'capability__in' => array( 'publish_posts' ),
-			'fields' => 'ID',
-		)
-	);
-
-	// we just need any user to generate a request signature
-	$user_id = \reset( $user );
 	$short_timeout = function() {
 		return 3;
 	};
 	add_filter( 'activitypub_remote_get_timeout', $short_timeout );
-	$response = Http::get( $actor, $user_id );
+	$response = Http::get( $actor );
 	remove_filter( 'activitypub_remote_get_timeout', $short_timeout );
 	if ( \is_wp_error( $response ) ) {
 		\set_transient( $transient_key, $response, HOUR_IN_SECONDS ); // Cache the error for a shorter period.

includes/model/class-user.php

@@ -0,0 +1,23 @@
+<?php
+namespace Activitypub\Model;
+
+/**
+ * ActivityPub User Class
+ *
+ * @author Matthias Pfefferle
+ */
+class User {
+	/**
+	 * The ID of the Blog User
+	 *
+	 * @var int
+	 */
+	const BLOG_USER_ID = 0;
+
+	/**
+	 * The ID of the Application User
+	 *
+	 * @var int
+	 */
+	const APPLICATION_USER_ID = -1;
+}

includes/rest/class-inbox.php

@@ -4,6 +4,7 @@ namespace Activitypub\Rest;
 use WP_Error;
 use WP_REST_Server;
 use WP_REST_Response;
+use Activitypub\Signature;
 use Activitypub\Model\Activity;
 
 use function Activitypub\get_context;
@@ -24,7 +25,6 @@ class Inbox {
 	 */
 	public static function init() {
 		\add_action( 'rest_api_init', array( self::class, 'register_routes' ) );
-		\add_filter( 'rest_pre_serve_request', array( self::class, 'serve_request' ), 11, 4 );
 
 		\add_action( 'activitypub_inbox_create', array( self::class, 'handle_create' ), 10, 2 );
 	}
@@ -66,35 +66,6 @@ class Inbox {
 		);
 	}
 
-	/**
-	 * Hooks into the REST API request to verify the signature.
-	 *
-	 * @param bool                      $served  Whether the request has already been served.
-	 * @param WP_HTTP_ResponseInterface $result  Result to send to the client. Usually a WP_REST_Response.
-	 * @param WP_REST_Request           $request Request used to generate the response.
-	 * @param WP_REST_Server            $server  Server instance.
-	 *
-	 * @return true
-	 */
-	public static function serve_request( $served, $result, $request, $server ) {
-		if ( '/activitypub' !== \substr( $request->get_route(), 0, 12 ) ) {
-			return $served;
-		}
-
-		$signature = $request->get_header( 'signature' );
-
-		if ( ! $signature ) {
-			return $served;
-		}
-
-		$headers = $request->get_headers();
-
-		// verify signature
-		//\Activitypub\Signature::verify_signature( $headers, $key );
-
-		return $served;
-	}
-
 	/**
 	 * Renders the user-inbox
 	 *
@@ -147,6 +118,7 @@ class Inbox {
 	 * @return WP_REST_Response
 	 */
 	public static function user_inbox_post( $request ) {
+
 		$user_id = $request->get_param( 'user_id' );
 
 		$data = $request->get_params();
@@ -167,6 +139,7 @@ class Inbox {
 	 * @return WP_REST_Response
 	 */
 	public static function shared_inbox_post( $request ) {
+
 		$data = $request->get_params();
 		$type = $request->get_param( 'type' );
 		$users = self::extract_recipients( $data );

includes/rest/class-server.php

@@ -0,0 +1,117 @@
+<?php
+namespace Activitypub\Rest;
+
+use stdClass;
+use WP_REST_Response;
+use Activitypub\Signature;
+use Activitypub\Model\User;
+
+use function Activitypub\get_context;
+use function Activitypub\get_rest_url_by_path;
+
+
+/**
+ * ActivityPub Server REST-Class
+ *
+ * @author Django Doucet
+ *
+ * @see https://www.w3.org/TR/activitypub/#security-verification
+ */
+class Server {
+
+	/**
+	 * Initialize the class, registering WordPress hooks
+	 */
+	public static function init() {
+		\add_action( 'rest_api_init', array( self::class, 'register_routes' ) );
+		\add_filter( 'rest_request_before_callbacks', array( self::class, 'authorize_activitypub_requests' ), 10, 3 );
+	}
+
+	/**
+	 * Register routes
+	 */
+	public static function register_routes() {
+		\register_rest_route(
+			ACTIVITYPUB_REST_NAMESPACE,
+			'/application',
+			array(
+				array(
+					'methods'             => \WP_REST_Server::READABLE,
+					'callback'            => array( self::class, 'application_actor' ),
+					'permission_callback' => '__return_true',
+				),
+			)
+		);
+	}
+
+	/**
+	 * Render Application actor profile
+	 *
+	 * @return WP_REST_Response The JSON profile of the Application Actor.
+	 */
+	public static function application_actor() {
+		$json = new stdClass();
+
+		$json->{'@context'} = get_context();
+		$json->id = get_rest_url_by_path( 'application' );
+		$json->type = 'Application';
+		$json->preferredUsername = str_replace( array( '.' ), '-', wp_parse_url( get_site_url(), PHP_URL_HOST ) ); // phpcs:ignore WordPress.NamingConventions
+		$json->name = get_bloginfo( 'name' );
+		$json->summary = __( 'WordPress-ActivityPub application actor', 'activitypub' );
+		$json->manuallyApprovesFollowers = true; // phpcs:ignore WordPress.NamingConventions
+		$json->icon = array( get_site_icon_url() ); // phpcs:ignore WordPress.NamingConventions short array syntax
+		$json->publicKey = array( // phpcs:ignore WordPress.NamingConventions
+			'id' => get_rest_url_by_path( 'application#main-key' ),
+			'owner' => get_rest_url_by_path( 'application' ),
+			'publicKeyPem' => Signature::get_public_key( User::APPLICATION_USER_ID ), // phpcs:ignore WordPress.NamingConventions
+		);
+
+		$response = new WP_REST_Response( $json, 200 );
+
+		$response->header( 'Content-Type', 'application/activity+json' );
+
+		return $response;
+	}
+
+	/**
+	 * Callback function to authorize each api requests
+	 *
+	 * @see WP_REST_Request
+	 *
+	 * @param WP_REST_Response|WP_HTTP_Response|WP_Error|mixed $response Result to send to the client.
+	 *                                                                   Usually a WP_REST_Response or WP_Error.
+	 * @param array                                            $handler  Route handler used for the request.
+	 * @param WP_REST_Request                                  $request  Request used to generate the response.
+	 *
+	 * @return mixed|WP_Error The response, error, or modified response.
+	 */
+	public static function authorize_activitypub_requests( $response, $handler, $request ) {
+		$route = $request->get_route();
+
+		// check if it is an activitypub request and exclude webfinger and nodeinfo endpoints
+		if (
+			! str_starts_with( $route, '/' . ACTIVITYPUB_REST_NAMESPACE ) ||
+			str_starts_with( $route, '/' . \trailingslashit( ACTIVITYPUB_REST_NAMESPACE ) . 'webfinger' ) ||
+			str_starts_with( $route, '/' . \trailingslashit( ACTIVITYPUB_REST_NAMESPACE ) . 'nodeinfo' )
+		) {
+			return $response;
+		}
+
+		// POST-Requets are always signed
+		if ( 'POST' === $request->get_method() ) {
+			$verified_request = Signature::verify_http_signature( $request );
+			if ( \is_wp_error( $verified_request ) ) {
+				return $verified_request;
+			}
+		} elseif ( 'GET' === $request->get_method() ) { // GET-Requests are only signed in secure mode
+			if ( ACTIVITYPUB_SECURE_MODE ) {
+				$verified_request = Signature::verify_http_signature( $request );
+				if ( \is_wp_error( $verified_request ) ) {
+					return $verified_request;
+				}
+			}
+		}
+
+		return $response;
+	}
+}

tests/test-class-activitypub-activity.php

@@ -22,7 +22,7 @@ class Test_Activitypub_Activity extends WP_UnitTestCase {
 		$activitypub_activity = new \Activitypub\Model\Activity( 'Create' );
 		$activitypub_activity->from_post( $activitypub_post );
 
-		$this->assertContains(  \Activitypub\get_rest_url_by_path( 'users/1/followers' ), $activitypub_activity->get_to() );
+		$this->assertContains( \Activitypub\get_rest_url_by_path( 'users/1/followers' ), $activitypub_activity->get_to() );
 		$this->assertContains( 'https://example.com/alex', $activitypub_activity->get_cc() );
 
 		remove_all_filters( 'activitypub_extract_mentions' );

tests/test-class-activitypub-rest-post-signature-verification.php

@@ -0,0 +1,110 @@
+<?php
+
+class Test_Activitypub_Signature_Verification extends WP_UnitTestCase {
+	public function test_activity_signature() {
+		// Activity for generate_digest
+		$post = \wp_insert_post(
+			array(
+				'post_author' => 1,
+				'post_content' => 'hello world',
+			)
+		);
+		$remote_actor = \get_author_posts_url( 2 );
+		$activitypub_post = new \Activitypub\Model\Post( $post );
+		$activitypub_activity = new Activitypub\Model\Activity( 'Create' );
+		$activitypub_activity->from_post( $activitypub_post );
+		$activitypub_activity->add_cc( $remote_actor );
+		$activity = $activitypub_activity->to_json();
+
+		// generate_digest & generate_signature
+		$digest = Activitypub\Signature::generate_digest( $activity );
+		$date = gmdate( 'D, d M Y H:i:s T' );
+		$signature = Activitypub\Signature::generate_signature( 1, 'POST', $remote_actor, $date, $digest );
+
+		$this->assertRegExp( '/keyId="http:\/\/example\.org\/\?author=1#main-key",algorithm="rsa-sha256",headers="\(request-target\) host date digest",signature="[^"]*"/', $signature );
+
+		//  Signed headers
+		$url_parts = wp_parse_url( $remote_actor );
+		$route = $url_parts['path'] . '?' . $url_parts['query'];
+		$host = $url_parts['host'];
+
+		$headers = array(
+			'digest' => array( $digest ),
+			'signature' => array( $signature ),
+			'date' => array( $date ),
+			'host' => array( $host ),
+			'(request-target)' => array( 'post ' . $route ),
+		);
+
+		// Start verification
+		// parse_signature_header, get_signed_data, get_public_key
+		$signature_block = Activitypub\Signature::parse_signature_header( $headers['signature'] );
+		$signed_headers = $signature_block['headers'];
+		$signed_data = Activitypub\Signature::get_signed_data( $signed_headers, $signature_block, $headers );
+
+		$public_key = Activitypub\Signature::get_public_key( 1 );
+
+		// signature_verification
+		$verified = \openssl_verify( $signed_data, $signature_block['signature'], $public_key, 'rsa-sha256' ) > 0;
+		$this->assertTrue( $verified );
+	}
+
+	public function test_rest_activity_signature() {
+		add_filter(
+			'pre_get_remote_metadata_by_actor',
+			function( $json, $actor ) {
+				// return ActivityPub Profile with signature
+				return array(
+					'id' => $actor,
+					'type' => 'Person',
+					'publicKey' => array(
+						'id' => $actor . '#main-key',
+						'owner' => $actor,
+						'publicKeyPem' => \Activitypub\Signature::get_public_key( 1 ),
+					),
+				);
+			},
+			10,
+			2
+		);
+
+		// Activity Object
+		$post = \wp_insert_post(
+			array(
+				'post_author' => 1,
+				'post_content' => 'hello world',
+			)
+		);
+		$remote_actor = \get_author_posts_url( 2 );
+		$remote_actor_inbox = Activitypub\get_rest_url_by_path( '/inbox' );
+		$activitypub_post = new \Activitypub\Model\Post( $post );
+		$activitypub_activity = new Activitypub\Model\Activity( 'Create' );
+		$activitypub_activity->from_post( $activitypub_post );
+		$activitypub_activity->add_cc( $remote_actor_inbox );
+		$activity = $activitypub_activity->to_json();
+
+		// generate_digest & generate_signature
+		$digest = Activitypub\Signature::generate_digest( $activity );
+		$date = gmdate( 'D, d M Y H:i:s T' );
+		$signature = Activitypub\Signature::generate_signature( 1, 'POST', $remote_actor_inbox, $date, $digest );
+
+		//  Signed headers
+		$url_parts = wp_parse_url( $remote_actor_inbox );
+		$route = $url_parts['path'] . '?' . $url_parts['query'];
+		$host = $url_parts['host'];
+
+		$request = new WP_REST_Request( 'POST', $route );
+		$request->set_header( 'content-type', 'application/activity+json' );
+		$request->set_header( 'digest', $digest );
+		$request->set_header( 'signature', $signature );
+		$request->set_header( 'date', $date );
+		$request->set_header( 'host', $host );
+		$request->set_body( $activity );
+
+		// Start verification
+		$verified = \Activitypub\Signature::verify_http_signature( $request );
+		$this->assertTrue( $verified );
+
+		remove_filter( 'pre_get_remote_metadata_by_actor', array( get_called_class(), 'pre_get_remote_key' ), 10, 2 );
+	}
+}