claude-code - 💡(How to fix) Fix Slack MCP (mcp.slack.com) fails: does not support dynamic client registration [2 comments, 2 participants]

The official Slack MCP server at https://mcp.slack.com/mcp cannot authenticate in Claude Code (CLI or desktop). Both the programmatic OAuth flow (mcp__slack__authenticate tool) and the /mcp UI dialog fail with the same error: 3. Try /mcp → select Slack → select "Authenticate" → same error 4. Try calling mcp__slack__authenticate tool programmatically → same error

TL;DR

The Slack MCP server authentication issue can be addressed by implementing a fallback in Claude Code's SDK to support static client registration for servers that do not support dynamic client registration.

Guidance

• Investigate modifying the Claude Code SDK to add support for static client registration as a fallback for servers like Slack's MCP that do not implement RFC 7591 Dynamic Client Registration.
• Verify the authentication flow with other MCP servers (e.g., Atlassian) to ensure the issue is specific to Slack's implementation.
• Consider using the slack-by-salesforce plugin as a temporary workaround for partial Slack functionality via skills.
• Review the RFC 7591 specification to understand the requirements for dynamic client registration and how it differs from static client registration.

Example

No code snippet is provided as the issue requires a high-level design change rather than a specific code fix.

Notes

The solution may require significant changes to the Claude Code SDK and may involve collaborating with the Slack team to understand their authentication requirements. The slack-by-salesforce plugin may not provide full functionality compared to the official Slack MCP server.

Recommendation

Apply a workaround by using the slack-by-salesforce plugin for partial Slack functionality, as implementing a fallback in the Claude Code SDK may require significant development and testing efforts.