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class-hmac-client.php
194 lines
| 1 | <?php |
| 2 | |
| 3 | /** |
| 4 | * HMAC Client for the Site Export API. |
| 5 | * |
| 6 | * This class generates the required HMAC signatures for authenticating |
| 7 | * requests to the Site Export API. The importing side uses this to sign |
| 8 | * all outgoing requests. |
| 9 | * |
| 10 | * Usage: |
| 11 | * $client = new Site_Export_HMAC_Client($shared_secret); |
| 12 | * $headers = $client->get_auth_headers($request_body); |
| 13 | * // Add $headers to your HTTP request |
| 14 | * |
| 15 | * Usage with curl: |
| 16 | * |
| 17 | * ```php |
| 18 | * // 1. First time: Generate and display a secret for the user |
| 19 | * $secret = Site_Export_HMAC_Client::generate_secret(); |
| 20 | * echo "Please enter this secret in the Site Export plugin settings:\n"; |
| 21 | * echo $secret . "\n"; |
| 22 | * |
| 23 | * // 2. For each request: Create client and sign requests |
| 24 | * $client = new Site_Export_HMAC_Client($secret); |
| 25 | * |
| 26 | * // For GET requests: |
| 27 | * $ch = curl_init('https://example.com/?reprint-api&endpoint=file_index&directory=/var/www/html'); |
| 28 | * $client->sign_curl_request($ch, ''); |
| 29 | * curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); |
| 30 | * $response = curl_exec($ch); |
| 31 | * |
| 32 | * // For POST requests with JSON body: |
| 33 | * $body = json_encode(['paths' => ['/wp-content/uploads/image.jpg']]); |
| 34 | * $ch = curl_init('https://example.com/?reprint-api&endpoint=file_fetch'); |
| 35 | * $client->sign_curl_request($ch, $body); |
| 36 | * curl_setopt($ch, CURLOPT_POST, true); |
| 37 | * curl_setopt($ch, CURLOPT_POSTFIELDS, $body); |
| 38 | * curl_setopt($ch, CURLOPT_HTTPHEADER, [ |
| 39 | * 'Content-Type: application/json', |
| 40 | * // Auth headers are added by sign_curl_request |
| 41 | * ]); |
| 42 | * $response = curl_exec($ch); |
| 43 | * ``` |
| 44 | */ |
| 45 | class Site_Export_HMAC_Client { |
| 46 | |
| 47 | /** |
| 48 | * Value of the X-Auth-Content-Hash header when the request body is |
| 49 | * deliberately not signed: this literal string stands where a body hash |
| 50 | * would otherwise be. Must match Site_Export_HMAC_Server::UNSIGNED_PAYLOAD. |
| 51 | */ |
| 52 | public const UNSIGNED_PAYLOAD = 'UNSIGNED-PAYLOAD'; |
| 53 | |
| 54 | /** @var string */ |
| 55 | private $secret; |
| 56 | |
| 57 | public function __construct(string $secret) { |
| 58 | $this->secret = $secret; |
| 59 | } |
| 60 | |
| 61 | /** Returns a hex-encoded random secret (64 chars = 256 bits by default). */ |
| 62 | public static function generate_secret(int $length = 32): string { |
| 63 | return bin2hex(random_bytes($length)); |
| 64 | } |
| 65 | |
| 66 | /** @return string Hex-encoded 16-byte nonce. */ |
| 67 | public function generate_nonce(): string { |
| 68 | return bin2hex(random_bytes(16)); |
| 69 | } |
| 70 | |
| 71 | /** @return string Microsecond-precision Unix timestamp. */ |
| 72 | public function get_timestamp(): string { |
| 73 | return sprintf('%.6f', microtime(true)); |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Compute the HMAC signature for a request. |
| 78 | * |
| 79 | * The signature covers a SHA-256 hash of the body rather than the raw |
| 80 | * bytes. This avoids having to predict the exact encoding that libcurl |
| 81 | * will produce for multipart/form-data uploads while still binding the |
| 82 | * request to a digest: the server verifies the timestamp, nonce, and HMAC |
| 83 | * over X-Auth-Content-Hash before it computes or compares any body hash. |
| 84 | * |
| 85 | * This is intended for small command requests such as preflight or plan |
| 86 | * confirmation. Large data transfers |
| 87 | * should use an authenticated session and per-chunk hashes instead of |
| 88 | * HMAC-signing one large request body. |
| 89 | * |
| 90 | * Signature = HMAC-SHA256(nonce + timestamp + SHA256(body), secret) |
| 91 | * |
| 92 | * @param string $nonce Random nonce for this request |
| 93 | * @param string $timestamp Request timestamp |
| 94 | * @param string $content_hash Hex SHA-256 hash of the request body |
| 95 | * @return string Hex-encoded HMAC signature |
| 96 | */ |
| 97 | public function compute_signature(string $nonce, string $timestamp, string $content_hash = ''): string { |
| 98 | if ($content_hash === '') { |
| 99 | $content_hash = hash('sha256', ''); |
| 100 | } |
| 101 | $message = $nonce . $timestamp . $content_hash; |
| 102 | return hash_hmac('sha256', $message, $this->secret); |
| 103 | } |
| 104 | |
| 105 | /** Returns all four X-Auth-* headers for a single request. */ |
| 106 | public function get_auth_headers(string $body = ''): array { |
| 107 | $nonce = $this->generate_nonce(); |
| 108 | $timestamp = $this->get_timestamp(); |
| 109 | $content_hash = hash('sha256', $body); |
| 110 | $signature = $this->compute_signature($nonce, $timestamp, $content_hash); |
| 111 | |
| 112 | return [ |
| 113 | 'X-Auth-Signature' => $signature, |
| 114 | 'X-Auth-Nonce' => $nonce, |
| 115 | 'X-Auth-Timestamp' => $timestamp, |
| 116 | 'X-Auth-Content-Hash' => $content_hash, |
| 117 | ]; |
| 118 | } |
| 119 | |
| 120 | /** |
| 121 | * Returns X-Auth-* headers for a request whose body is not signed. |
| 122 | * |
| 123 | * The signature covers the nonce, the timestamp, the method, and the |
| 124 | * request target instead of a body hash, so a body of any size streams |
| 125 | * through without either side hashing it, and captured auth headers still cannot be reused for a |
| 126 | * different endpoint or method. Protecting the body from tampering is |
| 127 | * TLS's job — over --force-http a tampered body would be accepted, |
| 128 | * which is what that flag's help text warns about. |
| 129 | * |
| 130 | * Signature = HMAC-SHA256(nonce + timestamp + "UNSIGNED-PAYLOAD\n" + METHOD + "\n" + target, secret) |
| 131 | * |
| 132 | * @param string $method Uppercased into the signature (GET, POST, ...). |
| 133 | * @param string $url Full request URL; only path and query are signed. |
| 134 | */ |
| 135 | public function get_envelope_auth_headers(string $method, string $url): array { |
| 136 | $nonce = $this->generate_nonce(); |
| 137 | $timestamp = $this->get_timestamp(); |
| 138 | $message = $nonce . $timestamp . self::UNSIGNED_PAYLOAD . "\n" . strtoupper($method) . "\n" . self::request_target($url); |
| 139 | |
| 140 | return [ |
| 141 | 'X-Auth-Signature' => hash_hmac('sha256', $message, $this->secret), |
| 142 | 'X-Auth-Nonce' => $nonce, |
| 143 | 'X-Auth-Timestamp' => $timestamp, |
| 144 | 'X-Auth-Content-Hash' => self::UNSIGNED_PAYLOAD, |
| 145 | ]; |
| 146 | } |
| 147 | |
| 148 | /** |
| 149 | * Normalizes a URL to the "path?query" form both sides sign — the same |
| 150 | * shape PHP exposes as $_SERVER['REQUEST_URI'] on the receiving end. |
| 151 | */ |
| 152 | public static function request_target(string $url): string { |
| 153 | $path = parse_url($url, PHP_URL_PATH); |
| 154 | $query = parse_url($url, PHP_URL_QUERY); |
| 155 | $target = is_string($path) && $path !== '' ? $path : '/'; |
| 156 | |
| 157 | return is_string($query) && $query !== '' ? $target . '?' . $query : $target; |
| 158 | } |
| 159 | |
| 160 | /** Returns auth headers formatted for CURLOPT_HTTPHEADER (["Name: value", ...]). */ |
| 161 | public function get_curl_headers(string $body = ''): array { |
| 162 | $headers = $this->get_auth_headers($body); |
| 163 | $curl_headers = []; |
| 164 | foreach ($headers as $name => $value) { |
| 165 | $curl_headers[] = "{$name}: {$value}"; |
| 166 | } |
| 167 | return $curl_headers; |
| 168 | } |
| 169 | |
| 170 | /** Sets CURLOPT_HTTPHEADER with auth headers on a cURL handle. */ |
| 171 | public function sign_curl_request($ch, string $body = ''): void { |
| 172 | curl_setopt($ch, CURLOPT_HTTPHEADER, $this->get_curl_headers($body)); |
| 173 | } |
| 174 | |
| 175 | /** Returns a stream context with auth headers, for use with file_get_contents(). */ |
| 176 | public function create_stream_context(string $body = '', string $method = 'GET', array $extra = []) { |
| 177 | $headers = $this->get_auth_headers($body); |
| 178 | $header_string = ''; |
| 179 | foreach ($headers as $name => $value) { |
| 180 | $header_string .= "{$name}: {$value}\r\n"; |
| 181 | } |
| 182 | |
| 183 | $options = [ |
| 184 | 'http' => array_merge([ |
| 185 | 'method' => $method, |
| 186 | 'header' => $header_string, |
| 187 | 'content' => $body, |
| 188 | ], $extra['http'] ?? []), |
| 189 | ]; |
| 190 | |
| 191 | return stream_context_create($options); |
| 192 | } |
| 193 | } |
| 194 |