One-click Slack MCP install: register official OAuth client

Bắt đầu từ luồng OAuth của cmd mcp add --transport http và so sánh metadata của máy chủ ủy quyền Slack với đường dẫn DCR Notion hiện có. Theo dõi nơi client dự phòng command-code được chọn và cách cấu hình chuyển hướng cục bộ http://127.0.0.1:8085/callback. Hoàn tất khi URL well-known của Slack mở phần ủy quyền Slack bằng một client chính thức và hoàn tất cài đặt mà không cần thông tin xác thực do người dùng tạo.

Summary

cmd mcp add --transport http slack https://mcp.slack.com/mcp cannot complete OAuth. Slack rejects the fallback client with Invalid client_id.

Root cause

Slack's MCP server (mcp.slack.com) does not advertise a Dynamic Client Registration endpoint in its OAuth authorization-server metadata:

{"issuer":"https://mcp.slack.com","authorization_endpoint":"https://slack.com/oauth/v2_user/authorize","token_endpoint":"https://slack.com/api/oauth.v2.user.access",...}

(compare Notion: mcp.notion.com advertises registration_endpoint and auto-registers fine).

When DCR is unavailable, the CLI falls back to a generic pre-registered client — clientId: "command-code" — which Slack rejects with Invalid client_id at https://slack.com/oauth/v2_user/authorize.

Expected behavior

One-click install like Claude/ChatGPT: user runs cmd mcp add slack https://mcp.slack.com/mcp, browser opens Slack's authorization page against an official, pre-registered Command Code Slack app, and completes.

Suggestion

Register an official Slack app (Slack "MCP connector" or custom app) with:

• OAuth redirect URL: http://127.0.0.1:8085/callback (the CLI's local callback)
• User scopes per Slack's MCP server scopes_supported (search:read., chat:write, channels:history, groups:history, im:history, mpim:history, canvases:read/write, users:read, reactions:, emoji:read, files:read/write, channels:read/write, groups:read/write, im:write, mpim:write, lists:read/write)

Then either ship clientId/clientSecret in the CLI for the well-known slack URL, or support server-keyed pre-registered credentials like other editors do.

Impact

Blocked install for the second most-requested MCP integration after Notion. Workaround today requires users to create their own Slack app and mcp add-json the client credentials.