fix: all oauth bugs fixed, manually tested

[aron-muon]

External OAuth Token Support

Summary

This PR adds support for external OAuth token providers, enabling the Slack MCP server to work with bearer tokens that weren't initiated by the application itself. This is useful for integrating with external identity providers or using pre-existing Slack tokens.

Changes

1. Workspace URL Capture and Usage

Problem: External tokens validated successfully via auth.test but subsequent API calls failed with invalid_auth because the Slack client was pointing to the wrong API endpoint (default https://slack.com/api/ instead of the workspace-specific URL like GovSlack or Enterprise Grid).

Solution:

• Added URL field to TokenInfo struct (pkg/oauth/types.go)
• Updated ValidateToken to capture the workspace URL from auth.test response (pkg/oauth/manager.go)
• Added URL field to UserContext (pkg/server/auth/context.go)
• Updated OAuth middleware to pass URL to context (pkg/server/auth/oauth_middleware.go)
• Updated all handlers to use slack.OptionAPIURL() when creating Slack clients (pkg/handler/channels.go, pkg/handler/conversations.go)

2. User Name Resolution in OAuth Mode

Problem: Messages displayed user IDs instead of usernames/display names in OAuth mode because the usersMap was always empty.

Solution:

• Added fetchUsersForMessages() helper function to fetch user info from Slack API
• Updated convertMessagesFromHistory and convertMessagesFromSearch to accept context and Slack client parameters
• Messages now show proper display names instead of user IDs

3. Channel Name to ID Resolution

Problem: Users couldn't use channel names like #general - they had to know the internal channel ID. In OAuth mode, this was especially problematic as the channel cache wasn't available.

Solution:

• Added resolveChannelName() helper function that:
  • Handles channel names with or without # prefix
  • Handles usernames with or without @ prefix for DM lookups
  • Falls back to Slack API for name resolution in OAuth mode
• Updated parseParamsToolConversations to accept context and Slack client
• Updated parseParamsToolSearch to resolve names for filter_users_from and filter_in_channel parameters

4. DM Channel Display Improvements

Problem: DM channels showed # instead of the username, and member counts were 0.

Solution:

• Updated channelsHandlerOAuth to detect DM channels (IsIM flag)
• Fetch user info via GetUserInfo API to display @username format
• Use GetUsersInConversation for group DMs (MPIMs) to get actual member count
• 1:1 DMs correctly show member count of 2

5. Search Results Channel Display

Problem: Search results showed channel IDs like #U1234567 for DMs instead of usernames.

Solution:

• Updated convertMessagesFromSearch to detect DM channel IDs (starting with 'D')
• Fetch user info when available to display @username format
• Fallback gracefully if user lookup fails

6. Slack Mention Text Processing

Problem: User mentions in message text showed concatenated text like U1UEU5QF0Ava Kopp without proper formatting.

Solution:

• Added regex handlers in filterSpecialChars() for Slack mention formats:
  • <@U1234567> → @U1234567
  • <@U1234567|displayname> → @displayname
  • <#C1234567> → #C1234567
  • <#C1234567|channel-name> → #channel-name

7. Defensive Programming

Problem: Nil pointer dereference when using channel names in OAuth mode because apiProvider was nil.

Solution:

• Added nil checks before accessing apiProvider in OAuth mode
• Clear error messages when channel/user resolution fails
• Graceful fallbacks throughout the codebase

Files Modified

• pkg/oauth/types.go - Added URL field to TokenInfo
• pkg/oauth/manager.go - Capture URL from auth.test response
• pkg/server/auth/context.go - Added URL field to UserContext
• pkg/server/auth/oauth_middleware.go - Pass URL to user context
• pkg/handler/channels.go - Use API URL, DM display improvements
• pkg/handler/conversations.go - User/channel resolution, name lookups
• pkg/text/text_processor.go - Slack mention formatting

Testing

• All existing unit tests pass
• Integration tests require Slack credentials (skipped in CI without tokens)
• Manual testing with external OAuth tokens confirmed working

Breaking Changes

None. All changes are backward compatible with existing token flow.

[aron-muon]

Closed for korotovsky#166 instead