MCP OAuth: No way to configure callback port, breaking Slack MCP and other services with fixed redirect URIs

[dulaj-me]

Description

OpenCode's remote MCP OAuth config (McpOAuthConfig) only supports clientId, clientSecret, and scope. There's no way to set a callbackPort or redirectUri.
OpenCode uses a random port for the OAuth callback (e.g. http://127.0.0.1:19876/mcp/oauth/callback), but services like Slack MCP (https://mcp.slack.com/mcp) require the redirect URI to exactly match a pre-registered URI. Since the port changes every time, auth always fails with:

redirect_uri did not match any configured URIs
This makes it impossible to use Slack MCP (and likely any remote MCP server that validates redirect URIs against a fixed allowlist).
Claude Code solves this by pinning the callback to port 3118 via a callbackPort config option.

Plugins

No response

OpenCode version

1.3.0

Steps to reproduce

1. Add Slack MCP to opencode.json:
   "slack": {
   "type": "remote",
   "url": "https://mcp.slack.com/mcp",
   "oauth": {
   "clientId": "1601185624273.8899143856786"
   }
   }
2. Run opencode mcp auth slack
3. Browser opens Slack OAuth page
4. Slack rejects with: redirect_uri did not match any configured URIs. Passed URI: http://127.0.0.1:<random_port>/mcp/oauth/callback

Expected: A callbackPort (or redirectUri) option in McpOAuthConfig so the callback port can be pinned, matching the registered redirect URI.

Screenshot and/or share link

Operating System

macOS 26.3.1 (a)

Terminal

Ghostty

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Allow custom OAuth redirect URI configuration for MCP servers #7377: Feature request for custom OAuth redirect URI configuration for MCP servers — covers the same root problem of OpenCode's hardcoded/random callback port breaking OAuth with providers that require exact redirect URI matches.

[dulaj-me]

Dang yeah. Closing. So sorry!