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Ole-Morten Duesund 8369ec2cc7 sec(oauth): phase-2 attack-path review (forgejo-mcp-broker-wgo) 
Structured review of every OAuth/auth handler against the standard
attack catalog. Findings table added to design.md §8.2.

Two real issues found and fixed:

  - Refresh-token replay race: tokenRefreshGrant read the row, validated
    it, then minted a new pair before unconditionally revoking the old
    refresh. Two concurrent /token requests with the same refresh would
    both pass validation and both mint a fresh pair — token-quota
    duplication and a hint to a stolen-refresh attacker. Fixed with the
    same atomic UPDATE rows-affected pattern already used for auth-code
    single-use. New TestToken_Refresh_ConcurrentReplay_OnlyOneSucceeds
    races two goroutines and verifies exactly one wins.

  - Permissive redirect_uri schemes: validateRedirectURI accepted any
    non-empty scheme, including javascript: and data:. Tightened to
    require https, http for loopback only, or a reverse-DNS private-use
    scheme per RFC 8252 §7.1. TestValidateRedirectURI updated to cover
    each variant including the rejected javascript:/data: cases.

Items deferred to backlog (already filed):
  - Rate limits on /oauth/register and /oauth/token (-ttl)
  - --token-fd to close the /proc/<pid>/environ window (-1n2)
  - AES-GCM at-rest encryption of Forgejo tokens (-sd4)

Closes forgejo-mcp-broker-wgo. Phase 2 complete.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-27 17:37:00 +02:00
.beads sec(oauth): phase-2 attack-path review (forgejo-mcp-broker-wgo) 2026-04-27 17:37:00 +02:00
.claude bd init: initialize beads issue tracking 2026-04-24 16:34:50 +02:00
cmd/broker feat(cmd/broker): wire config → log → store → httpserver (forgejo-mcp-broker-t37) 2026-04-24 17:29:37 +02:00
docs sec(oauth): phase-2 attack-path review (forgejo-mcp-broker-wgo) 2026-04-27 17:37:00 +02:00
internal sec(oauth): phase-2 attack-path review (forgejo-mcp-broker-wgo) 2026-04-27 17:37:00 +02:00
.gitignore bd init: initialize beads issue tracking 2026-04-24 16:34:50 +02:00
AGENTS.md bd init: initialize beads issue tracking 2026-04-24 16:34:50 +02:00
CLAUDE.md docs: fill CLAUDE.md with phase-1 session learnings 2026-04-24 17:37:36 +02:00
go.mod feat(store): SQLite with embedded migrations (forgejo-mcp-broker-9jh) 2026-04-24 17:22:47 +02:00
go.sum feat(store): SQLite with embedded migrations (forgejo-mcp-broker-9jh) 2026-04-24 17:22:47 +02:00
LICENSE bd init: initialize beads issue tracking 2026-04-24 16:34:50 +02:00
Makefile feat: bootstrap Go project layout (forgejo-mcp-broker-n84) 2026-04-24 16:54:27 +02:00
README.md bd init: initialize beads issue tracking 2026-04-24 16:34:50 +02:00

README.md

forgejo-mcp-broker

OAuth 2.1 authorization server and MCP session broker for forgejo-mcp.

Lets MCP clients such as Claude.ai connect to a Forgejo instance through a single public HTTPS endpoint, with per-user authentication delegated to Forgejo's own OAuth2 provider. The broker handles the OAuth dance, then spawns a dedicated forgejo-mcp --transport stdio subprocess for each authenticated session, scoped to the authenticated user's Forgejo access token.

Status: Planning. No code yet. See docs/design.md for the architecture and docs/plan.md for the phased implementation plan.

How it fits

Claude.ai ──HTTPS──▶ Caddy ──▶ fjmcp-broker ──stdio──▶ forgejo-mcp  ──▶ Forgejo API
                                  (this)              (one per user     (per-user
                                                       session)          token)
  • fjmcp-broker (this project): one long-running process. Handles OAuth discovery, dynamic client registration, the authorization-code flow against Forgejo, session lifecycle, and stdio-to-streamable-HTTP bridging.
  • forgejo-mcp (existing project): used as-is. Spawned per-session with the authenticated user's FORGEJO_ACCESS_TOKEN in the environment.
  • Caddy: terminates TLS for the public hostname and reverse-proxies to the broker.

Why a broker instead of adding OAuth to forgejo-mcp?

Process-level isolation. Each user's Forgejo token lives in exactly one subprocess — the broker never needs to demultiplex tokens inside a single shared client. This keeps forgejo-mcp's sync.Once singleton-client pattern valid and avoids a refactor of every tool handler. Full trade-off in docs/design.md.

Quick map

File What
docs/design.md Architecture, components, token flow, deployment, security
docs/plan.md Seven-phase implementation plan with acceptance criteria

License

MIT © 2026 Ole-Morten Duesund.