Connect Claude Code to Slack MCP through a custom Slack app

Hello,

Is it possible to configure a custom MySlack app (not Claude app) to connect from ClaudeCode to Slack MCP?
I was trying configuring my own app and then using that app's clientId in the MCP configuration like below:

{
  "mcpServers": {
    "slack": {
      "type": "http",
      "url": "https://mcp.slack.com/mcp",
      "oauth": {
        "clientId": "myClientId",
        "callbackPort": 3118
      }
    }
  }
}

The error I get back says "redirect_uri did not match any configured URIs. Passed URI: http://localhost:3118/callback".
But when I try registering http://localhost:3118/callback in my app's configuration, I'm not able to do it because of Please use a complete URL beginning with https (for security) error which blocks registering http redirects.

Can someone explain if it's even possible and how to do it correctly?

Start by reviewing the MCP configuration shown in the issue and the Slack app OAuth redirect URI requirements. Document whether a custom Slack app is supported, how the localhost callback should be configured, and what the completed setup should look like.