security: PKCE S256 verification + redirect_uri allowlist + JWT access tokens

includes/MCP/OAuthServer.php

@@ -4,31 +4,41 @@ namespace AskTamMCP\MCP;
 
 defined('ABSPATH') || exit;
 
+/**
+ * OAuth 2.0 server with:
+ *   - PKCE (S256) verification on token exchange
+ *   - redirect_uri allowlist per key
+ *   - Short-lived JWT access tokens (not raw API keys)
+ *   - authorization_code + client_credentials grants
+ */
 class OAuthServer {
 
+    // Allowed redirect_uri origins — Claude.ai callback
+    private const ALLOWED_REDIRECT_HOSTS = [
+        'claude.ai',
+        'localhost',
+        '127.0.0.1',
+    ];
+
     public function registerRoutes(): void {
-        // Authorization endpoint
         register_rest_route('asktam-mcp/v1', '/oauth/authorize', [
             'methods'             => ['GET', 'POST'],
             'callback'            => [$this, 'handleAuthorize'],
             'permission_callback' => '__return_true',
         ]);
 
-        // Token endpoint
         register_rest_route('asktam-mcp/v1', '/oauth/token', [
             'methods'             => 'POST',
             'callback'            => [$this, 'handleToken'],
             'permission_callback' => '__return_true',
         ]);
 
-        // Metadata
         register_rest_route('asktam-mcp/v1', '/oauth/metadata', [
             'methods'             => 'GET',
             'callback'            => [$this, 'handleMetadata'],
             'permission_callback' => '__return_true',
         ]);
 
-        // Well-known
         add_action('rest_api_init', function () {
             register_rest_route('', '/.well-known/oauth-authorization-server', [
                 'methods'             => 'GET',
@@ -39,15 +49,22 @@ class OAuthServer {
     }
 
     // -------------------------------------------------------------------------
-    // Authorization endpoint — must output raw HTML and die, bypassing REST wrapper
+    // Authorization endpoint
     // -------------------------------------------------------------------------
     public function handleAuthorize(\WP_REST_Request $request): void {
-        $clientId    = sanitize_text_field($request->get_param('client_id')    ?? '');
+        $clientId      = sanitize_text_field($request->get_param('client_id')             ?? '');
-        $redirectUri = esc_url_raw($request->get_param('redirect_uri')         ?? '');
+        $redirectUri   = esc_url_raw($request->get_param('redirect_uri')                  ?? '');
-        $state       = sanitize_text_field($request->get_param('state')        ?? '');
+        $state         = sanitize_text_field($request->get_param('state')                 ?? '');
-        $approved    = sanitize_text_field($request->get_param('_mcp_approve') ?? '');
+        $codeChallenge = sanitize_text_field($request->get_param('code_challenge')        ?? '');
+        $challengeMethod = sanitize_text_field($request->get_param('code_challenge_method') ?? 'S256');
+        $approved      = sanitize_text_field($request->get_param('_mcp_approve')          ?? '');
 
-        // Validate client_id
+        // 1. Validate redirect_uri host
+        if (!$this->isRedirectUriAllowed($redirectUri)) {
+            wp_die('Invalid redirect_uri: host not in allowlist.', 'MCP Security Error', ['response' => 400]);
+        }
+
+        // 2. Validate client_id
         global $wpdb;
         $table = $wpdb->prefix . 'asktam_mcp_keys';
         $row   = $wpdb->get_row(
@@ -56,111 +73,34 @@ class OAuthServer {
         );
 
         if (!$row) {
-            // Send user back with error
+            $this->redirectError($redirectUri, 'invalid_client', $state);
-            if ($redirectUri) {
+            return;
-                wp_redirect(add_query_arg(['error' => 'invalid_client', 'state' => $state], $redirectUri));
-                exit;
-            }
-            status_header(401);
-            header('Content-Type: text/plain');
-            echo 'Invalid client_id. Check your API key in WP Admin → AskTam MCP.';
-            exit;
         }
 
-        // POST: user clicked Approve
+        // 3. PKCE: require code_challenge for authorization_code flow
+        if (empty($codeChallenge)) {
+            $this->redirectError($redirectUri, 'invalid_request', $state, 'PKCE code_challenge is required');
+            return;
+        }
+
+        // 4. POST: user approved
         if ($_SERVER['REQUEST_METHOD'] === 'POST' && $approved === '1') {
             $code = 'mcp_code_' . bin2hex(random_bytes(16));
             set_transient('asktam_mcp_code_' . $code, [
-                'client_id'    => $clientId,
+                'client_id'        => $clientId,
-                'redirect_uri' => $redirectUri,
+                'redirect_uri'     => $redirectUri,
-                'scopes'       => $row['scopes'],
+                'scopes'           => $row['scopes'],
-            ], 300);
+                'key_id'           => $row['id'],
+                'code_challenge'   => $codeChallenge,
+                'challenge_method' => $challengeMethod,
+            ], 300); // 5 min
 
             wp_redirect(add_query_arg(['code' => $code, 'state' => $state], $redirectUri));
             exit;
         }
 
-        // GET: render approval page — output raw HTML, bypass REST JSON wrapper
+        // 5. GET: render approval page
-        $siteName  = get_bloginfo('name');
+        $this->renderApprovalPage($row, $clientId, $redirectUri, $state, $codeChallenge, $challengeMethod);
-        $keyName   = esc_html($row['name']);
-        $scopes    = array_map('trim', explode(',', $row['scopes']));
-        $actionUrl = rest_url('asktam-mcp/v1/oauth/authorize');
-
-        // Send correct headers BEFORE any output
-        status_header(200);
-        header('Content-Type: text/html; charset=UTF-8');
-        header('X-Robots-Tag: noindex');
-        // Remove REST API JSON headers that WP might have set
-        header_remove('Content-Type'); // remove any previously set
-        header('Content-Type: text/html; charset=UTF-8');
-
-        // Output and die — this prevents WP REST from wrapping in JSON
-        ob_end_clean();
-        ?>
-<!DOCTYPE html>
-<html lang="en">
-<head>
-    <meta charset="UTF-8">
-    <meta name="viewport" content="width=device-width, initial-scale=1">
-    <title>Authorize — <?php echo esc_html($siteName); ?></title>
-    <style>
-        * { box-sizing: border-box; margin: 0; padding: 0; }
-        body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif; background: #f0f2f5; display: flex; align-items: center; justify-content: center; min-height: 100vh; padding: 20px; }
-        .card { background: #fff; border-radius: 16px; box-shadow: 0 4px 32px rgba(0,0,0,.12); max-width: 420px; width: 100%; padding: 40px 36px; }
-        .logo { display: flex; align-items: center; gap: 12px; margin-bottom: 32px; }
-        .logo strong { font-size: 17px; color: #1a1a1a; }
-        h2 { font-size: 22px; color: #1a1a1a; margin-bottom: 10px; }
-        p { color: #666; font-size: 14px; line-height: 1.65; margin-bottom: 22px; }
-        .key-box { background: #f8f9ff; border: 1.5px solid #d0d9ff; border-radius: 10px; padding: 16px 18px; margin-bottom: 28px; }
-        .key-box .lbl { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: .6px; color: #888; margin-bottom: 5px; }
-        .key-box .val { font-size: 15px; font-weight: 700; color: #1a1a1a; margin-bottom: 10px; }
-        .scopes { display: flex; flex-wrap: wrap; gap: 6px; }
-        .scope { background: #ede9fe; color: #5b21b6; border-radius: 5px; padding: 3px 10px; font-size: 12px; font-weight: 600; }
-        .btns { display: flex; gap: 10px; }
-        .btn { flex: 1; padding: 13px; border-radius: 9px; border: none; font-size: 15px; font-weight: 700; cursor: pointer; transition: opacity .15s; }
-        .btn:active { opacity: .8; }
-        .approve { background: #2271b1; color: #fff; }
-        .deny { background: #f5f5f5; color: #444; border: 1.5px solid #ddd; }
-        .note { margin-top: 22px; font-size: 12px; color: #aaa; text-align: center; line-height: 1.5; }
-    </style>
-</head>
-<body>
-<div class="card">
-    <div class="logo">
-        <svg width="36" height="36" viewBox="0 0 36 36" fill="none"><circle cx="18" cy="18" r="18" fill="#2271b1"/><path d="M11 26L18 11L25 26" stroke="white" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/><path d="M13.5 21H22.5" stroke="white" stroke-width="2.5" stroke-linecap="round"/></svg>
-        <strong>AskTam MCP &mdash; <?php echo esc_html($siteName); ?></strong>
-    </div>
-
-    <h2>Authorize Access</h2>
-    <p>An AI client is requesting access to your WordPress site using this API key:</p>
-
-    <div class="key-box">
-        <div class="lbl">API Key</div>
-        <div class="val"><?php echo $keyName; ?></div>
-        <div class="scopes">
-            <?php foreach ($scopes as $s): ?>
-                <span class="scope"><?php echo esc_html($s); ?></span>
-            <?php endforeach; ?>
-        </div>
-    </div>
-
-    <form method="post" action="<?php echo esc_url($actionUrl); ?>">
-        <input type="hidden" name="client_id"    value="<?php echo esc_attr($clientId); ?>">
-        <input type="hidden" name="redirect_uri" value="<?php echo esc_attr($redirectUri); ?>">
-        <input type="hidden" name="state"        value="<?php echo esc_attr($state); ?>">
-        <input type="hidden" name="_mcp_approve" value="1">
-        <div class="btns">
-            <button type="submit" class="btn approve">Approve</button>
-            <button type="button" class="btn deny" onclick="window.location='<?php echo esc_js(add_query_arg(['error' => 'access_denied', 'state' => $state], $redirectUri)); ?>'">Deny</button>
-        </div>
-    </form>
-
-    <div class="note">Only approve if you initiated this connection from Claude.ai or another trusted MCP client.</div>
-</div>
-</body>
-</html>
-        <?php
-        exit;
     }
 
     // -------------------------------------------------------------------------
@@ -169,18 +109,17 @@ class OAuthServer {
     public function handleToken(\WP_REST_Request $request): \WP_REST_Response {
         $grantType = $request->get_param('grant_type') ?? '';
 
-        if ($grantType === 'authorization_code') {
+        return match ($grantType) {
-            return $this->handleAuthCodeExchange($request);
+            'authorization_code'  => $this->handleAuthCodeExchange($request),
-        }
+            'client_credentials'  => $this->handleClientCredentials($request),
-        if ($grantType === 'client_credentials') {
+            default               => $this->oauthError('unsupported_grant_type', 'Supported: authorization_code, client_credentials', 400),
-            return $this->handleClientCredentials($request);
+        };
-        }
-
-        return $this->oauthError('unsupported_grant_type', 'Supported: authorization_code, client_credentials', 400);
     }
 
     private function handleAuthCodeExchange(\WP_REST_Request $request): \WP_REST_Response {
-        $code = $request->get_param('code') ?? '';
+        $code         = $request->get_param('code')          ?? '';
+        $codeVerifier = $request->get_param('code_verifier') ?? '';
+        $redirectUri  = $request->get_param('redirect_uri')  ?? '';
 
         if (empty($code)) {
             return $this->oauthError('invalid_request', 'Missing code', 400);
@@ -191,18 +130,52 @@ class OAuthServer {
             return $this->oauthError('invalid_grant', 'Authorization code expired or invalid', 400);
         }
 
+        // Always delete — one-time use
         delete_transient('asktam_mcp_code_' . $code);
 
-        [$clientId] = $this->extractCredentials($request);
+        // PKCE verification
-        if (!empty($clientId) && $clientId !== $codeData['client_id']) {
+        if (!empty($codeData['code_challenge'])) {
-            return $this->oauthError('invalid_client', 'client_id mismatch', 401);
+            if (empty($codeVerifier)) {
+                return $this->oauthError('invalid_grant', 'PKCE code_verifier is required', 400);
+            }
+
+            $method    = $codeData['challenge_method'] ?? 'S256';
+            $challenge = $codeData['code_challenge'];
+
+            $valid = match ($method) {
+                'S256'  => hash_equals($challenge, rtrim(strtr(base64_encode(hash('sha256', $codeVerifier, true)), '+/', '-_'), '=')),
+                'plain' => hash_equals($challenge, $codeVerifier),
+                default => false,
+            };
+
+            if (!$valid) {
+                return $this->oauthError('invalid_grant', 'PKCE verification failed', 400);
+            }
         }
 
+        // redirect_uri must match what was used in /authorize
+        if (!empty($codeData['redirect_uri']) && $redirectUri !== $codeData['redirect_uri']) {
+            return $this->oauthError('invalid_grant', 'redirect_uri mismatch', 400);
+        }
+
+        // Fetch key row and issue JWT
+        global $wpdb;
+        $row = $wpdb->get_row(
+            $wpdb->prepare("SELECT * FROM {$wpdb->prefix}asktam_mcp_keys WHERE id = %d AND is_active = 1", $codeData['key_id']),
+            ARRAY_A
+        );
+
+        if (!$row) {
+            return $this->oauthError('invalid_grant', 'Key no longer active', 400);
+        }
+
+        $accessToken = \AskTamMCP\Core\TokenManager::issue($row);
+
         return new \WP_REST_Response([
-            'access_token' => $codeData['client_id'],
+            'access_token' => $accessToken,
             'token_type'   => 'bearer',
-            'expires_in'   => 3600 * 24 * 30,
+            'expires_in'   => 3600,
-            'scope'        => $codeData['scopes'],
+            'scope'        => $row['scopes'],
         ], 200);
     }
 
@@ -214,9 +187,8 @@ class OAuthServer {
         }
 
         global $wpdb;
-        $table = $wpdb->prefix . 'asktam_mcp_keys';
+        $row = $wpdb->get_row(
-        $row   = $wpdb->get_row(
+            $wpdb->prepare("SELECT * FROM {$wpdb->prefix}asktam_mcp_keys WHERE api_key = %s AND is_active = 1", $clientId),
-            $wpdb->prepare("SELECT * FROM {$table} WHERE api_key = %s AND is_active = 1", $clientId),
             ARRAY_A
         );
 
@@ -224,8 +196,10 @@ class OAuthServer {
             return $this->oauthError('invalid_client', 'Invalid credentials', 401);
         }
 
+        $accessToken = \AskTamMCP\Core\TokenManager::issue($row);
+
         return new \WP_REST_Response([
-            'access_token' => $clientId,
+            'access_token' => $accessToken,
             'token_type'   => 'bearer',
             'expires_in'   => 3600,
             'scope'        => $row['scopes'],
@@ -250,8 +224,45 @@ class OAuthServer {
     }
 
     // -------------------------------------------------------------------------
-    // Helpers
+    // Security helpers
     // -------------------------------------------------------------------------
+
+    /**
+     * Validate redirect_uri against an allowlist of trusted hosts.
+     * Only claude.ai and localhost are allowed by default.
+     * Filterable for custom setups.
+     */
+    private function isRedirectUriAllowed(string $uri): bool {
+        if (empty($uri)) return false;
+
+        $host = parse_url($uri, PHP_URL_HOST);
+        if (!$host) return false;
+
+        $allowed = apply_filters('asktam_mcp_allowed_redirect_hosts', self::ALLOWED_REDIRECT_HOSTS);
+
+        foreach ($allowed as $allowedHost) {
+            // Exact match or subdomain match
+            if ($host === $allowedHost || str_ends_with($host, '.' . $allowedHost)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private function redirectError(string $redirectUri, string $error, string $state, string $description = ''): void {
+        if ($redirectUri && $this->isRedirectUriAllowed($redirectUri)) {
+            $params = ['error' => $error, 'state' => $state];
+            if ($description) $params['error_description'] = $description;
+            wp_redirect(add_query_arg($params, $redirectUri));
+            exit;
+        }
+        status_header(400);
+        header('Content-Type: text/plain');
+        echo "OAuth error: {$error}";
+        exit;
+    }
+
     private function extractCredentials(\WP_REST_Request $request): array {
         $clientId     = $request->get_param('client_id');
         $clientSecret = $request->get_param('client_secret');
@@ -260,9 +271,9 @@ class OAuthServer {
             return [$clientId, $clientSecret];
         }
 
-        $authHeader = $request->get_header('Authorization');
+        $auth = $request->get_header('Authorization');
-        if ($authHeader && str_starts_with($authHeader, 'Basic ')) {
+        if ($auth && str_starts_with($auth, 'Basic ')) {
-            $decoded = base64_decode(substr($authHeader, 6));
+            $decoded = base64_decode(substr($auth, 6));
             if ($decoded && str_contains($decoded, ':')) {
                 [$clientId, $clientSecret] = explode(':', $decoded, 2);
                 return [trim($clientId), trim($clientSecret)];
@@ -273,9 +284,92 @@ class OAuthServer {
     }
 
     private function oauthError(string $error, string $description, int $status): \WP_REST_Response {
-        return new \WP_REST_Response([
+        return new \WP_REST_Response(['error' => $error, 'error_description' => $description], $status);
-            'error'             => $error,
+    }
-            'error_description' => $description,
+
-        ], $status);
+    // -------------------------------------------------------------------------
+    // Approval page UI
+    // -------------------------------------------------------------------------
+    private function renderApprovalPage(array $row, string $clientId, string $redirectUri, string $state, string $codeChallenge, string $challengeMethod): void {
+        $siteName  = get_bloginfo('name');
+        $keyName   = esc_html($row['name']);
+        $scopes    = array_map('trim', explode(',', $row['scopes']));
+        $actionUrl = rest_url('asktam-mcp/v1/oauth/authorize');
+
+        while (ob_get_level()) ob_end_clean();
+        status_header(200);
+        header('Content-Type: text/html; charset=UTF-8');
+        header('X-Robots-Tag: noindex');
+        ?>
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <title>Authorize — <?php echo esc_html($siteName); ?></title>
+    <style>
+        * { box-sizing: border-box; margin: 0; padding: 0; }
+        body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif; background: #f0f2f5; display: flex; align-items: center; justify-content: center; min-height: 100vh; padding: 20px; }
+        .card { background: #fff; border-radius: 16px; box-shadow: 0 4px 32px rgba(0,0,0,.12); max-width: 420px; width: 100%; padding: 40px 36px; }
+        .logo { display: flex; align-items: center; gap: 12px; margin-bottom: 32px; }
+        .logo strong { font-size: 17px; color: #1a1a1a; }
+        h2 { font-size: 22px; color: #1a1a1a; margin-bottom: 10px; }
+        p { color: #666; font-size: 14px; line-height: 1.65; margin-bottom: 22px; }
+        .key-box { background: #f8f9ff; border: 1.5px solid #d0d9ff; border-radius: 10px; padding: 16px 18px; margin-bottom: 28px; }
+        .key-box .lbl { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: .6px; color: #888; margin-bottom: 5px; }
+        .key-box .val { font-size: 15px; font-weight: 700; color: #1a1a1a; margin-bottom: 10px; }
+        .scopes { display: flex; flex-wrap: wrap; gap: 6px; }
+        .scope { background: #ede9fe; color: #5b21b6; border-radius: 5px; padding: 3px 10px; font-size: 12px; font-weight: 600; }
+        .security-note { background: #fff8ed; border: 1px solid #f5d87a; border-radius: 8px; padding: 10px 14px; margin-bottom: 20px; font-size: 12px; color: #7a5c00; }
+        .btns { display: flex; gap: 10px; }
+        .btn { flex: 1; padding: 13px; border-radius: 9px; border: none; font-size: 15px; font-weight: 700; cursor: pointer; }
+        .approve { background: #2271b1; color: #fff; }
+        .deny { background: #f5f5f5; color: #444; border: 1.5px solid #ddd; }
+        .note { margin-top: 20px; font-size: 12px; color: #aaa; text-align: center; line-height: 1.5; }
+    </style>
+</head>
+<body>
+<div class="card">
+    <div class="logo">
+        <svg width="36" height="36" viewBox="0 0 36 36" fill="none"><circle cx="18" cy="18" r="18" fill="#2271b1"/><path d="M11 26L18 11L25 26" stroke="white" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/><path d="M13.5 21H22.5" stroke="white" stroke-width="2.5" stroke-linecap="round"/></svg>
+        <strong>AskTam MCP &mdash; <?php echo esc_html($siteName); ?></strong>
+    </div>
+
+    <h2>Authorize Access</h2>
+    <p>An AI client is requesting access to your WordPress site using this API key:</p>
+
+    <div class="key-box">
+        <div class="lbl">API Key</div>
+        <div class="val"><?php echo $keyName; ?></div>
+        <div class="scopes">
+            <?php foreach ($scopes as $s): ?>
+                <span class="scope"><?php echo esc_html($s); ?></span>
+            <?php endforeach; ?>
+        </div>
+    </div>
+
+    <div class="security-note">
+        🔒 Access token expires in <strong>1 hour</strong>. Your API key is never shared with the client.
+    </div>
+
+    <form method="post" action="<?php echo esc_url($actionUrl); ?>">
+        <input type="hidden" name="client_id"          value="<?php echo esc_attr($clientId); ?>">
+        <input type="hidden" name="redirect_uri"        value="<?php echo esc_attr($redirectUri); ?>">
+        <input type="hidden" name="state"               value="<?php echo esc_attr($state); ?>">
+        <input type="hidden" name="code_challenge"      value="<?php echo esc_attr($codeChallenge); ?>">
+        <input type="hidden" name="code_challenge_method" value="<?php echo esc_attr($challengeMethod); ?>">
+        <input type="hidden" name="_mcp_approve"        value="1">
+        <div class="btns">
+            <button type="submit" class="btn approve">Approve</button>
+            <button type="button" class="btn deny" onclick="window.location='<?php echo esc_js(add_query_arg(['error' => 'access_denied', 'state' => $state], $redirectUri)); ?>'">Deny</button>
+        </div>
+    </form>
+
+    <div class="note">Only approve if you initiated this from Claude.ai or a trusted MCP client.</div>
+</div>
+</body>
+</html>
+        <?php
+        exit;
     }
 }