refactor: use validateAuthorizationParameters in handleOAuthPar

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

src/pds.js

···
     const codeChallengeMethod = data.code_challenge_method;
     const loginHint = data.login_hint;
 
-    if (!clientId)
-      return errorResponse('invalid_request', 'client_id required', 400);
-    if (!redirectUri)
-      return errorResponse('invalid_request', 'redirect_uri required', 400);
-    if (responseType !== 'code')
-      return errorResponse(
-        'unsupported_response_type',
-        'response_type must be code',
-        400,
-      );
-    if (!codeChallenge || codeChallengeMethod !== 'S256') {
-      return errorResponse('invalid_request', 'PKCE with S256 required', 400);
-    }
-
-    let clientMetadata;
-    try {
-      clientMetadata = await getClientMetadata(clientId);
-    } catch (err) {
-      return errorResponse('invalid_client', err.message, 400);
-    }
-
-    // Validate redirect_uri against registered URIs
-    // For loopback clients (RFC 8252), allow any path on the same origin
-    const isLoopback =
-      clientId.startsWith('http://localhost') ||
-      clientId.startsWith('http://127.0.0.1');
-    const redirectUriValid = clientMetadata.redirect_uris.some((uri) => {
-      if (isLoopback) {
-        // For loopback, check origin match (any path allowed)
-        try {
-          const registered = new URL(uri);
-          const requested = new URL(redirectUri);
-          return registered.origin === requested.origin;
-        } catch {
-          return false;
-        }
-      }
-      return uri === redirectUri;
+    // Use shared validation
+    const validationResult = await this.validateAuthorizationParameters({
+      clientId,
+      redirectUri,
+      responseType,
+      codeChallenge,
+      codeChallengeMethod,
     });
-    if (!redirectUriValid) {
-      return errorResponse(
-        'invalid_request',
-        'redirect_uri not registered for this client',
-        400,
-      );
-    }
+    if ('error' in validationResult) return validationResult.error;
+    const { clientMetadata } = validationResult;
 
     const requestId = crypto.randomUUID();
     const requestUri = `urn:ietf:params:oauth:request_uri:${requestId}`;