AegisGitea-MCP/README.md

# AegisGitea-MCP

Security-first MCP server for self-hosted Gitea with per-user OAuth2/OIDC authentication for Claude, Claude Code, and Cowork.

AegisGitea-MCP exposes MCP tools over Streamable HTTP and a legacy SSE alias. Each user authenticates with Gitea through OAuth2/OIDC; repository authorization is checked per user before any service PAT call is allowed.

## Securing MCP with Gitea OAuth

This guide uses the live deployment values as the running example:

| Thing | Value |
|-------|-------|
| Gitea instance (`GITEA_URL`) | `https://git.hiddenden.cafe` |
| This MCP server (`PUBLIC_BASE_URL`) | `https://gitea-mcp.hiddenden.cafe` |
| OAuth callback to register in Gitea | `https://gitea-mcp.hiddenden.cafe/oauth/callback` |
| MCP URL you give to Claude | `https://gitea-mcp.hiddenden.cafe/mcp` |

Substitute your own hostnames if they differ. The two URLs are **different hosts**: `git.*` is Gitea, `gitea-mcp.*` is this proxy.

### 1) Create a Gitea OAuth2 application

1. Open `https://git.hiddenden.cafe/user/settings/applications` (or admin application settings).
2. Create an OAuth2 app.
3. Set the redirect URI to **this MCP server's callback** (not Gitea's own host):
   `https://gitea-mcp.hiddenden.cafe/oauth/callback`
   This is the only redirect URI Gitea needs — the MCP server forwards each client's real callback through a signed state parameter.
4. Save the app and copy the generated `Client ID` and `Client Secret`.

Required scopes:
- `read:repository`
- `write:repository` (only needed when using write tools)

### 2) Configure this MCP server

```bash
cp .env.example .env
```

Fill in exactly these values in `.env` (everything else has safe defaults):

```env
# The Gitea instance this server talks to
GITEA_URL=https://git.hiddenden.cafe

# Per-user OAuth mode (recommended)
OAUTH_MODE=true
GITEA_OAUTH_CLIENT_ID=<client-id-from-step-1>
GITEA_OAUTH_CLIENT_SECRET=<client-secret-from-step-1>

# Public URL of THIS server (no trailing slash). Claude's MCP URL is this + /mcp
PUBLIC_BASE_URL=https://gitea-mcp.hiddenden.cafe

# Secret that signs the OAuth proxy state. Generate with: openssl rand -hex 32
OAUTH_STATE_SECRET=<random-32-byte-minimum-secret>

# Where dynamically-registered OAuth clients are stored — MUST be a writable,
# persistent path. The default matches the aegis-mcp-data volume in compose.
DCR_STORAGE_PATH=/var/lib/aegis-mcp/dcr_clients.json
```

### 2b) Service PAT (`GITEA_TOKEN`) — needed in practice

Gitea issues **OIDC access tokens** that carry only `openid/profile/email`. They establish identity but **cannot call the repository REST API**, so in pure-OAuth mode most tools fail (you will see a generic error, or `list_repositories` returning nothing usable). Configure a service PAT so the tools actually work:

1. Create a **dedicated bot account** in Gitea (not a personal account).
2. Generate a Personal Access Token with least privilege:
   - `read:repository`
   - `write:repository` only if you enable `WRITE_MODE`
3. Set it in `.env`:

```env
GITEA_TOKEN=<bot-personal-access-token>
```

This does **not** weaken per-user security. OAuth remains authoritative: before every repository call the server verifies that the signed-in user has permission on the target repo through Gitea (`_verify_user_repository_access`) and denies it otherwise. The PAT only performs the API call after that check; OAuth provides identity, per-user authorization, and audit attribution.

Note: with a service PAT, `list_repositories` is intentionally blocked because it has no repository target to authorize per user — use the repository-scoped tools (`get_repository_info`, `get_file_contents`, `list_issues`, …) instead.

### 2a) Required writable volumes (read-only container)

The provided `docker-compose.yml` runs the container with a **read-only root filesystem**. The server therefore needs two writable volumes, both already wired up in compose:

| Path | Purpose | Volume |
|------|---------|--------|
| `/var/log/aegis-mcp` | tamper-evident audit log | `aegis-mcp-logs` |
| `/var/lib/aegis-mcp` | dynamic client registration store (`DCR_STORAGE_PATH`) | `aegis-mcp-data` |

If `/var/lib/aegis-mcp` is **not** writable/persistent, the OAuth `authorize`, `token`, and `register` endpoints fail and the browser shows a bare `Internal Server Error` during login. Keep the `aegis-mcp-data` volume mounted (or point `DCR_STORAGE_PATH` at another writable, persistent location), and make sure it survives restarts so registered clients are not lost.

### 3) Configure Claude, Claude Code, or Cowork

Claude's hosted, desktop, mobile, Claude Code, and Cowork surfaces share the same remote MCP connector infrastructure. There is no Claude-specific server code path.

In claude.ai:

1. Open **Settings > Connectors**.
2. Choose **Add custom connector**.
3. Paste `https://gitea-mcp.hiddenden.cafe/mcp`.
4. Complete the OAuth consent flow. Dynamic Client Registration (`/register`) handles Claude client registration.

In Claude Code:

```bash
claude mcp add --transport http aegis-gitea https://gitea-mcp.hiddenden.cafe/mcp
```

Cowork uses the same connector model and MCP URL.

Manual OAuth client configuration remains available for clients that do not use DCR:

- MCP server URL: `https://gitea-mcp.hiddenden.cafe/mcp`
- Authentication: OAuth
- OAuth client ID: the client id returned by `/register` or your preconfigured client id
- OAuth client secret: only for confidential clients

Hosted Claude callbacks are allowed by default: `https://claude.ai/api/mcp/auth_callback` and `https://claude.com/api/mcp/auth_callback`. Loopback redirects for Claude Code local development are allowed for `http://127.0.0.1:*` and `http://localhost:*`.

### 4) OAuth-protected MCP behavior

The server publishes protected-resource metadata:

- `GET /.well-known/oauth-protected-resource`

Example response:

```json
{
  "resource": "https://gitea-mcp.hiddenden.cafe",
  "authorization_servers": [
    "https://gitea-mcp.hiddenden.cafe",
    "https://git.hiddenden.cafe"
  ],
  "bearer_methods_supported": ["header"],
  "scopes_supported": ["read:repository", "write:repository"],
  "resource_documentation": "https://hiddenden.cafe/docs/mcp-gitea"
}
```

If a tool call is missing/invalid auth, MCP endpoints return `401` with:

```http
WWW-Authenticate: Bearer resource_metadata="https://<mcp-host>/.well-known/oauth-protected-resource", scope="read:repository"
```

## Architecture

```text
Claude / Claude Code / Cowork
  -> Authorization Code Flow
  -> Gitea OAuth2/OIDC (issuer: https://git.hiddenden.cafe)
  -> Access token
   -> MCP Server (/mcp, /mcp/sse, /mcp/tool/call)
     -> OIDC discovery + JWKS cache
     -> Scope enforcement (read:repository / write:repository)
     -> Policy allow/deny
     -> If GITEA_TOKEN is set: check Gitea collaborator permission for <user, repo>
     -> Gitea API call with either the user token or the service PAT after authz
```

## Example curl

Protected resource metadata:

```bash
curl -s https://<mcp-host>/.well-known/oauth-protected-resource | jq
```

Expected 401 challenge when missing token:

```bash
curl -i https://<mcp-host>/mcp/tool/call \
  -H "Content-Type: application/json" \
  -d '{"tool":"list_repositories","arguments":{}}'
```

Authenticated tool call:

```bash
curl -s https://<mcp-host>/mcp/tool/call \
  -H "Authorization: Bearer <user_access_token>" \
  -H "Content-Type: application/json" \
  -d '{"tool":"get_repository_info","arguments":{"owner":"acme","repo":"demo"}}'
```

## Threat model

- Shared bot tokens are dangerous:
  - one leaked token can expose all repositories reachable by that bot account.
  - blast radius is repository-wide and cross-user.
- Token-in-URL is insecure:
  - URLs leak via logs, proxies, browser history, and referers.
  - bearer tokens must be sent in `Authorization` headers only.
- Per-user OAuth reduces lateral access:
  - identity comes from Gitea OIDC/JWKS or userinfo validation.
  - without `GITEA_TOKEN`, API calls use the user's token and Gitea enforces permissions.
  - with `GITEA_TOKEN`, every repository-targeted call first checks the user's Gitea permission and fails closed if the check cannot be made.

## CI/CD

Gitea workflows were added under `.gitea/workflows/`:

- `lint.yml`: Ruff + formatting + mypy.
- `test.yml`: lint + pytest + enforced coverage (`>=80%`).
- `docker.yml`: lint+test gated Docker build, SHA tag, `latest` tag on `main`.

## Docker hardening

`docker/Dockerfile` uses a multi-stage build, non-root runtime user, production env flags, minimal runtime dependencies, and a healthcheck.

## Commands

- `make test`
- `make lint`
- `make format`
- `make docker-build`
- `make docker-up`

## Documentation

- `docs/api-reference.md`
- `docs/security.md`
- `docs/configuration.md`
- `docs/deployment.md`
- `docs/write-mode.md`