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<?php |
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/** |
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* Signature class file. |
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* |
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* @package Activitypub |
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*/ |
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|
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namespace Activitypub; |
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|
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use Activitypub\Signature\Http_Message_Signature; |
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use Activitypub\Signature\Http_Signature_Draft; |
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|
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/** |
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* ActivityPub Signature Class. |
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* |
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* @author Matthias Pfefferle |
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* @author Django Doucet |
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*/ |
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class Signature { |
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|
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/** |
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* Initialize the class. |
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*/ |
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public static function init() { |
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\add_filter( 'http_request_args', array( self::class, 'sign_request' ), 0, 2 ); // Ahead of all other filters, so signature is set. |
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\add_filter( 'http_response', array( self::class, 'maybe_double_knock' ), 10, 3 ); |
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} |
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|
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/** |
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* Sign an HTTP Request. |
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* |
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* @param array $args An array of HTTP request arguments. |
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* @param string $url The request URL. |
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* |
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* @return array Request arguments with signature headers. |
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*/ |
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public static function sign_request( $args, $url ) { |
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// Bail if there's nothing to sign with. |
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if ( ! isset( $args['key_id'], $args['private_key'] ) ) { |
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return $args; |
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} |
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|
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if ( '1' === \get_option( 'activitypub_rfc9421_signature' ) && self::could_support_rfc9421( $url ) ) { |
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$signature = new Http_Message_Signature(); |
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} else { |
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$signature = new Http_Signature_Draft(); |
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} |
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|
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return $signature->sign( $args, $url ); |
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} |
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|
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/** |
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* Verifies the http signatures |
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* |
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* On success the verified keyId is returned (a truthy string), so callers can bind it to |
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* the activity actor without re-parsing headers, which cannot tell which signature label |
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* actually validated. Pass/fail callers should branch on {@see is_wp_error()} as before. |
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* |
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* @since 9.0.0 Returns the verified keyId on success instead of `true`. |
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* |
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* @param \WP_REST_Request|array $request The request object or $_SERVER array. |
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* |
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* @return string|\WP_Error The verified keyId on success, WP_Error on failure. |
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*/ |
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public static function verify_http_signature( $request ) { |
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if ( is_object( $request ) ) { // REST Request object. |
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$body = $request->get_body(); |
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$headers = $request->get_headers(); |
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$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' ' . self::get_route( $request ); |
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} else { |
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$headers = self::format_server_request( $request ); |
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$headers['(request-target)'][0] = strtolower( $headers['request_method'][0] ) . ' ' . $headers['request_uri'][0]; |
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} |
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|
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$signature = isset( $headers['signature_input'] ) ? new Http_Message_Signature() : new Http_Signature_Draft(); |
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|
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return $signature->verify( $headers, $body ?? null ); |
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} |
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|
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/** |
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* Extract the signing keyId that {@see Signature::verify_http_signature()} would verify against. |
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* |
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* The returned keyId is only trustworthy if it identifies the key the signature is |
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* actually checked with, so this mirrors the verifier's header choice rather than |
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* scanning headers in an arbitrary order: |
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* |
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* - When a `Signature-Input` header is present the RFC 9421 verifier is used, so the |
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* keyId is taken from there and a draft `Signature` header (which the verifier ignores) |
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* is not consulted. The RFC 9421 verifier accepts whichever of several signature labels |
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* validates, so a `Signature-Input` carrying more than one keyId is ambiguous: we cannot |
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* know in advance which key will verify and must not guess, so `null` is returned. |
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* - Otherwise the draft HTTP Signatures form is used, taking the first `keyId` from the |
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* `Signature` header or, failing that, the `Authorization` header — matching the draft |
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* verifier, which reads `signature ?? authorization`. |
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* |
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* @since 9.0.0 |
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* |
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* @param \WP_REST_Request $request The request object. |
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* |
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* @return string|null The keyId, or null when none is present or the choice is ambiguous. |
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*/ |
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public static function get_key_id( $request ) { |
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$signature_input = $request->get_header( 'signature-input' ); |
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if ( $signature_input ) { |
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/* |
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* keyid is a `;`-delimited parameter whose value may be quoted or unquoted. |
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* Anchoring on `;` (or string start) avoids matching a `keyid=` substring inside |
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* another parameter's value. Count every label's keyId: more than one is ambiguous. |
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*/ |
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$count = \preg_match_all( '/(?:^|;)\s*keyid="?([^";,\s]+)/i', $signature_input, $matches ); |
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|
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return 1 === $count ? $matches[1][0] : null; |
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} |
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|
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// A draft signature may arrive in the Signature header or, less commonly, Authorization. |
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$signature = $request->get_header( 'signature' ); |
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if ( ! $signature ) { |
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$signature = $request->get_header( 'authorization' ); |
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} |
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|
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if ( $signature && \preg_match( '/keyId="([^"]+)"/i', $signature, $matches ) ) { |
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return $matches[1]; |
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} |
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|
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return null; |
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} |
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|
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/** |
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* If a request with RFC-9421 signature fails, we try again with the Draft Cavage signature. |
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* |
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* @param array $response HTTP response. |
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* @param array $args HTTP request arguments. |
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* @param string $url The request URL. |
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* |
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* @return array The HTTP response. |
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*/ |
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public static function maybe_double_knock( $response, $args, $url ) { |
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// Bail if it didn't use an RFC-9421 signature or there's nothing to sign with. |
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if ( ! isset( $args['key_id'], $args['private_key'], $args['headers']['Signature-Input'] ) ) { |
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return $response; |
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} |
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|
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$response_code = \wp_remote_retrieve_response_code( $response ); |
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|
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// Fall back to Draft Cavage signature for any 4xx responses. |
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if ( $response_code >= 400 && $response_code < 500 ) { |
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unset( $args['headers']['Signature'], $args['headers']['Signature-Input'], $args['headers']['Content-Digest'] ); |
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self::rfc9421_add_unsupported_host( $url ); |
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|
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$args = ( new Http_Signature_Draft() )->sign( $args, $url ); |
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$response = \wp_safe_remote_request( $url, $args ); |
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} |
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|
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return $response; |
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} |
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|
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/** |
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* Formats the $_SERVER to resemble the WP_REST_REQUEST array, |
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* for use with verify_http_signature(). |
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* |
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* @param array $server The $_SERVER array. |
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* |
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* @return array $request The formatted request array. |
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*/ |
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public static function format_server_request( $server ) { |
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$headers = array(); |
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|
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foreach ( $server as $key => $value ) { |
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$key = \str_replace( 'http_', '', \strtolower( $key ) ); |
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$headers[ $key ][] = \wp_unslash( $value ); |
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|
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} |
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|
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return $headers; |
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} |
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|
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/** |
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* Returns route. |
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* |
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* @param \WP_REST_Request $request The request object. |
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* |
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* @return string |
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*/ |
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private static function get_route( $request ) { |
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// Check if the route starts with "index.php". |
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if ( str_starts_with( $request->get_route(), '/index.php' ) || ! rest_get_url_prefix() ) { |
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$route = $request->get_route(); |
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} else { |
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$route = '/' . rest_get_url_prefix() . '/' . ltrim( $request->get_route(), '/' ); |
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} |
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|
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// Fix route for subdirectory installations. |
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$path = \wp_parse_url( \get_home_url(), PHP_URL_PATH ); |
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|
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if ( \is_string( $path ) ) { |
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$path = trim( $path, '/' ); |
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} |
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|
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if ( $path ) { |
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$route = '/' . $path . $route; |
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} |
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|
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/* |
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* Append the query string. Peers sign the full request-target including |
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* the query (see Http_Signature_Draft::sign()), so the reconstructed |
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* value has to match byte-for-byte. Use the raw REQUEST_URI instead of |
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* re-encoding the parsed query params, re-encoding could change the |
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* percent-encoding or parameter order and break the signature. |
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*/ |
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// phpcs:ignore WordPress.Security.ValidatedSanitizedInput |
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$query = (string) \wp_parse_url( $_SERVER['REQUEST_URI'] ?? '', \PHP_URL_QUERY ); |
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|
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if ( '' !== $query ) { |
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$route .= '?' . $query; |
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} |
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|
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return $route; |
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} |
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|
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/** |
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* Check if RFC-9421 signature could be supported. |
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* |
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* @param string $url The URL to check. |
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* |
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* @return bool True, if RFC-9421 signature could be supported, false otherwise. |
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*/ |
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private static function could_support_rfc9421( $url ) { |
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$host = \wp_parse_url( $url, \PHP_URL_HOST ); |
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$list = \get_option( 'activitypub_rfc9421_unsupported', array() ); |
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|
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if ( isset( $list[ $host ] ) ) { |
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if ( $list[ $host ] > \time() ) { |
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return false; |
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} |
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|
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unset( $list[ $host ] ); |
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\update_option( 'activitypub_rfc9421_unsupported', $list ); |
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} |
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|
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return true; |
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} |
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|
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/** |
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* Set RFC-9421 signature unsupported for a given host. |
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* |
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* @param string $url The URL to set. |
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*/ |
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private static function rfc9421_add_unsupported_host( $url ) { |
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$list = \get_option( 'activitypub_rfc9421_unsupported', array() ); |
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$host = \wp_parse_url( $url, \PHP_URL_HOST ); |
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|
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$list[ $host ] = \time() + MONTH_IN_SECONDS; |
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\update_option( 'activitypub_rfc9421_unsupported', $list, false ); |
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} |
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|
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/** |
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* Compute the collection digest for a specific instance. |
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* |
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* Implements FEP-8fcf: Followers collection synchronization. |
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* The digest is created by XORing together the individual SHA256 digests |
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* of each follower's ID. |
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* |
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* @see https://codeberg.org/fediverse/fep/src/branch/main/fep/8fcf/fep-8fcf.md |
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* |
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* @param array $collection The user ID whose followers to compute. |
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* |
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* @return string|false The hex-encoded digest, or false if no followers. |
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*/ |
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public static function get_collection_digest( $collection ) { |
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if ( empty( $collection ) || ! is_array( $collection ) ) { |
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return false; |
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} |
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|
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// Initialize with zeros (64 hex chars = 32 bytes = 256 bits). |
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$digest = str_repeat( '0', 64 ); |
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|
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foreach ( $collection as $item ) { |
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// Compute SHA256 hash of the follower ID. |
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$hash = hash( 'sha256', $item ); |
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|
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// XOR the hash with the running digest. |
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$digest = self::xor_hex_strings( $digest, $hash ); |
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} |
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|
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return $digest; |
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} |
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|
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/** |
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* XOR two hexadecimal strings. |
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* |
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* Used for FEP-8fcf digest computation. |
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* |
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* @param string $hex1 First hex string. |
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* @param string $hex2 Second hex string. |
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* |
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* @return string The XORed result as a hex string. |
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*/ |
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public static function xor_hex_strings( $hex1, $hex2 ) { |
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$result = ''; |
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|
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// Ensure both strings are the same length (should be 64 chars for SHA256). |
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$length = \max( \strlen( $hex1 ), \strlen( $hex2 ) ); |
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$hex1 = \str_pad( $hex1, $length, '0', STR_PAD_LEFT ); |
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$hex2 = \str_pad( $hex2, $length, '0', STR_PAD_LEFT ); |
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|
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// XOR each pair of hex digits. |
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for ( $i = 0; $i < $length; $i += 2 ) { |
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$byte1 = \hexdec( \substr( $hex1, $i, 2 ) ); |
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$byte2 = \hexdec( \substr( $hex2, $i, 2 ) ); |
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$result .= \str_pad( \dechex( $byte1 ^ $byte2 ), 2, '0', STR_PAD_LEFT ); |
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} |
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|
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return $result; |
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} |
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|
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/** |
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* Parse a Collection-Synchronization header (FEP-8fcf). |
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* |
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* Parses the signature-style format used by the Collection-Synchronization header. |
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* |
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* @see https://codeberg.org/fediverse/fep/src/branch/main/fep/8fcf/fep-8fcf.md |
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* |
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* @param string $header The header value. |
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* |
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* @return array|false Array with parsed parameters (collectionId, url, digest), or false on failure. |
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*/ |
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public static function parse_collection_sync_header( $header ) { |
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if ( empty( $header ) ) { |
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return false; |
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} |
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|
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// Parse the signature-style format: key="value", key="value". |
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$params = array(); |
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|
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if ( \preg_match_all( '/(\w+)="([^"]*)"/', $header, $matches, PREG_SET_ORDER ) ) { |
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foreach ( $matches as $match ) { |
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$params[ $match[1] ] = $match[2]; |
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} |
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} |
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|
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// Validate required fields for FEP-8fcf. |
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if ( empty( $params['collectionId'] ) || empty( $params['url'] ) || empty( $params['digest'] ) ) { |
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return false; |
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} |
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|
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return $params; |
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} |
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} |
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|
