Slack MCP Server Authentication issue

[neeltom92]

Issue Summary

The Slack MCP server provided by the productivity plugin fails to authenticate with error: "Incompatible auth server: does not support dynamic client registration"

Error Details

When attempting to authenticate with the Slack MCP server through the Claude Code, the following error occurs:

Plugin: productivity:slack MCP Server
Status: ✘ failed
Auth: ✘ not authenticated
URL: https://mcp.slack.com/mcp
Config location: Dynamically configured

Error: Incompatible auth server: does not support dynamic client registration

Configuration

Current Slack MCP Configuration

{
  "mcpServers": {
    "slack": {
      "type": "http",
      "url": "https://mcp.slack.com/mcp"
    }
  }
}

Root Cause

Slack's OAuth server does not support Dynamic Client Registration (DCR), which Claude Code appears to attempt by default for HTTP-based MCP servers. Slack requires pre-registered OAuth applications with explicit client credentials.

Expected Behavior

One of the following should occur:

1. Plugin pre-configuration: The productivity plugin should either:

   • Include pre-registered OAuth credentials for Slack
   • Detect DCR incompatibility and guide users through manual OAuth setup
   • Provide clear documentation on setting up OAuth credentials

2. Graceful fallback: Claude Code should detect when DCR is not supported and:

   • Prompt the user to register an OAuth app
   • Provide step-by-step instructions
   • Offer to add the credentials via CLI

3. Better error messaging: The error should explain:

   • Why authentication failed
   • What the user needs to do
   • Link to documentation or setup guide