Does Claude.ai support MCP OAuth authorization (2025-06-18)? Getting 'Tool execution failed' instead of OAuth flow

[matsonwade]

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• I have checked that this question would not be more appropriate as an issue in a specific repository
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Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

Does Claude.ai support the latest version 2025-06-18 MCP authorization protocol? My remote MCP server returns a 401 with WWW-Authenticate: Bearer resource_metadata="PRM URL", yet Claude.ai responds with "Tool execution failed" instead of initiating the OAuth flow.

Context for my MCP Server:

• MCP TypeScript SDK 1.17.3
• Streamable HTTP based on latest 2025-06-18 protocol
• Successfully completes MCP Inspector's OAuth flow
• Endpoint is https://mcp.sitesparq-dev.io/mcp
• Deployed on AWS Fargate (ECS) behind ALB + CloudFront

To reproduce, you can call curl with:

curl -i -sS "https://mcp.sitesparq-dev.io/mcp" -X POST -H 'Content-Type: application/json' --data-binary @- <<'JSON'
{"jsonrpc":"2.0","id":"1","method":"tools/call","params":{"name":"get_website","arguments":{"websiteId":"65b7addb-a549-4953-b4df-b4d165cbe802"},"stream":false}}
JSON

Here's the response:

HTTP/1.1 401 Unauthorized
Content-Length: 0
Connection: keep-alive
Date: Wed, 01 Oct 2025 21:35:17 GMT
Set-Cookie: AWSALBAPP-0=remove; Expires=Wed, 08 Oct 2025 21:35:17 GMT; Path=/
Set-Cookie: AWSALBAPP-1=remove; Expires=Wed, 08 Oct 2025 21:35:17 GMT; Path=/
Set-Cookie: AWSALBAPP-2=remove; Expires=Wed, 08 Oct 2025 21:35:17 GMT; Path=/
Set-Cookie: AWSALBAPP-3=remove; Expires=Wed, 08 Oct 2025 21:35:17 GMT; Path=/
X-Powered-By: Express
Access-Control-Allow-Origin: *
Vary: Origin
Access-Control-Allow-Headers: Content-Type, Authorization, MCP-Session-Id
Access-Control-Expose-Headers: WWW-Authenticate
Access-Control-Allow-Methods: GET, POST, DELETE, OPTIONS
WWW-Authenticate: Bearer resource_metadata="https://mcp.sitesparq-dev.io/.well-known/oauth-protected-resource"
X-Cache: Error from cloudfront
Via: 1.1 027f3e9868eb8f82bc6ad5eae363a2fa.cloudfront.net (CloudFront)
X-Amz-Cf-Pop: SFO53-P6
X-Amz-Cf-Id: QDzQtmTGB4zX9nvlxsCgy_aDt8m3pGSSU2hGIDE8kR2IOgkbzdvRQA==