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mcp-nextcloud/docs/auth-flows.md
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Chris CoutinhoandClaude Opus 4.7 319e82774e docs: correct OIDC architecture framing for Login Flow v2 
The previous round of review feedback rested on a misunderstanding —
that the MCP server is "the OAuth issuer" under Login Flow v2 and that
NEXTCLOUD_OIDC_CLIENT_ID/SECRET are external-IdP-only. Code says
otherwise (app.py:619/625/703-717, unified_verifier.py:72):

- The MCP server is an OIDC relying party of Nextcloud OIDC. Tokens are
  signed by Nextcloud and validated against Nextcloud's JWKS in all
  modes — the server has no private signing keys.
- Static NEXTCLOUD_OIDC_CLIENT_ID/SECRET are the preferred way to
  register the MCP server as that relying party; RFC 7591 DCR is a
  fallback when both are unset.
- Login Flow v2 layers per-user app-password acquisition on top — it
  governs the MCP→Nextcloud data leg, not the relying-party setup.

This commit reverts the inaccuracies introduced by 35c115e and reframes
the original `login-flow-v2.md` to match what the code does:

- login-flow-v2.md: revise "How It Works" to describe the MCP server
  as an OIDC RP + OAuth facade (not a standalone issuer); rename
  "OAuth Issuer Endpoints" → "OAuth Endpoints" with a note that those
  endpoints front Nextcloud OIDC; add NEXTCLOUD_OIDC_CLIENT_ID/SECRET
  to the required env vars with DCR documented as fallback.
- running.md: restore the static-creds Docker example (deleted in
  35c115e on the wrong reasoning that it was tied to the retired
  direct-OAuth-to-Nextcloud flow); rewrite the OAuth Mode section
  intro to describe the actual relying-party + facade architecture.
- configuration.md: fix Best Practices "For Production" to mention
  static creds as preferred / DCR as fallback; restore the .oauth
  Docker volume alongside data so DCR-registered MCP-client state and
  the encrypted app-password DB both persist.
- auth-flows.md: drop the note added in 35c115e that wrongly claimed
  the MCP server validates Bearer tokens against its own JWKS under
  Login Flow v2 — it validates against Nextcloud's JWKS in all modes;
  reword the Login Flow v2 "Key characteristics" bullet that called
  the MCP server "the OAuth authorization server".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-30 02:29:01 +02:00

13 KiB
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Authentication Flows by Deployment Mode

This document provides a unified reference for the auth flows in each supported deployment mode. For configuration details, see Authentication. For Login Flow v2 architecture and setup, see Login Flow v2.

Quick Reference Matrix

Mode Client → MCP → NC Background Sync Astrolabe → MCP
Single-User BasicAuth Embedded credentials Same credentials N/A
Multi-User BasicAuth Header pass-through Stored app password (optional) OAuth Bearer token
Login Flow v2 OAuth → MCP, app pwd → NC Stored app password OAuth Bearer token

Communication Patterns

This document covers three distinct communication patterns:

  1. MCP Client → MCP Server → Nextcloud: Interactive tool calls initiated by users through MCP clients (Claude Desktop, claude.ai, custom clients).
  2. MCP Server → Nextcloud: Background operations like vector sync that run without user interaction.
  3. Astrolabe → MCP Server: Astrolabe app backend communication for settings UI and unified search.

Deployment Modes

1. Single-User BasicAuth

Use Case: Personal Nextcloud instance, local development, single-user deployments.

MCP Client → MCP Server → Nextcloud

MCP Client                    MCP Server                   Nextcloud
    │                             │                            │
    │── MCP Request ─────────────▶│                            │
    │   (no auth required)        │                            │
    │                             │── HTTP + BasicAuth ───────▶│
    │                             │   Authorization: Basic     │
    │                             │   (embedded credentials)   │
    │                             │◀── API Response ───────────│
    │◀── Tool Result ─────────────│                            │

Key characteristics:

  • Credentials embedded in server configuration (NEXTCLOUD_USERNAME, NEXTCLOUD_PASSWORD)
  • Single shared NextcloudClient created at startup
  • No MCP-level authentication required (server trusts local clients)
  • All requests use the same Nextcloud user

Implementation: context.py — returns the shared client from lifespan context

Background Sync

Uses the same embedded credentials as interactive requests. The background job accesses Nextcloud with the configured username/password.

Astrolabe Integration

Not applicable — Astrolabe is only used in multi-user deployments where users need personal settings and per-user state.

2. Multi-User BasicAuth

Use Case: Internal deployment where users provide their own Nextcloud credentials via HTTP headers.

MCP Client → MCP Server → Nextcloud

MCP Client                    MCP Server                   Nextcloud
    │                             │                            │
    │── MCP Request ─────────────▶│                            │
    │   Authorization: Basic      │                            │
    │   (user credentials)        │                            │
    │                             │── BasicAuthMiddleware ────▶│
    │                             │   Extracts credentials     │
    │                             │                            │
    │                             │── HTTP + BasicAuth ───────▶│
    │                             │   (pass-through)           │
    │                             │◀── API Response ───────────│
    │◀── Tool Result ─────────────│                            │

Key characteristics:

  • BasicAuthMiddleware extracts credentials from the Authorization: Basic header
  • Credentials passed through to Nextcloud (not stored)
  • Client created per-request from extracted credentials
  • Stateless — no credential storage between requests

Background Sync (Optional)

If users provision an app password (via Astrolabe or nc_auth_provision_access), the server can run background jobs on their behalf:

Astrolabe                     MCP Server                   Nextcloud
    │                             │                            │
    │── Store app password ──────▶│                            │
    │   (via management API)      │                            │
    │                             │ [Encrypt + persist locally]│
    │                             │  (SQLite, Fernet)          │
    │◀── Confirmation ────────────│                            │
    │                             │                            │
    │         [Background job]    │                            │
    │                             │── Retrieve app password ──▶│
    │                             │── HTTP + BasicAuth ───────▶│
    │                             │◀── API Response ───────────│

Requirements: TOKEN_ENCRYPTION_KEY, TOKEN_STORAGE_DB.

Astrolabe → MCP Server

Astrolabe                     MCP Server                   Nextcloud OIDC
    │                             │                            │
    │── OAuth Flow ──────────────▶│◀── Token from IdP ────────▶│
    │   (user initiates)          │                            │
    │                             │                            │
    │── Bearer Token ────────────▶│                            │
    │   (management API calls)    │                            │
    │                             │── Validate via JWKS ──────▶│
    │                             │   (or introspection)       │
    │◀── API Response ────────────│                            │

Key characteristics:

  • Astrolabe has its own OAuth client registered in Nextcloud
  • Tokens are validated by the MCP server using Nextcloud OIDC JWKS
  • Authorization check: token.sub == requested_resource_owner
  • The same JWKS-based validation path applies under Login Flow v2 — the MCP server is an OIDC relying party of Nextcloud OIDC in both modes; Login Flow v2 only changes the MCP→Nextcloud credential leg (per-user app passwords).

3. Login Flow v2

Use Case: Hosted multi-user deployments, OAuth-based MCP clients (claude.ai, Astrolabe Cloud), production. Recommended for any setup where MCP clients shouldn't handle Nextcloud credentials directly.

This mode replaces the previously-supported "OAuth Single-Audience" and "OAuth Token Exchange" modes, both of which required upstream Nextcloud patches that were never merged. See ADR-022 for the rationale.

MCP Client → MCP Server → Nextcloud (steady state)

MCP Client                    MCP Server                   Nextcloud
    │                             │                            │
    │── Bearer Token ────────────▶│                            │
    │   (issued by MCP server,    │                            │
    │    mcp:* scopes)            │                            │
    │                             │── Validate scopes ─────────│
    │                             │   (@require_scopes)        │
    │                             │                            │
    │                             │── Lookup user's            │
    │                             │   stored app password      │
    │                             │                            │
    │                             │── HTTP + BasicAuth ───────▶│
    │                             │   Authorization: Basic     │
    │                             │   (per-user app password)  │
    │                             │◀── API Response ───────────│
    │◀── Tool Result ─────────────│                            │

Key characteristics:

  • MCP client authenticates to MCP server via OAuth 2.1 + PKCE
  • MCP server is an OIDC relying party of Nextcloud OIDC + an OAuth facade for MCP clients (RFC 7591 DCR for MCP-client registration; the server's own RP credentials come from NEXTCLOUD_OIDC_CLIENT_ID/SECRET, with DCR fallback). Tokens are signed by Nextcloud OIDC and validated against Nextcloud's JWKS.
  • mcp:* scopes (e.g. mcp:notes.read, mcp:notes.write) gate tool access
  • Per-user app password obtained via Login Flow v2 and stored encrypted in SQLite
  • App passwords appear in Nextcloud's Settings → Security → Devices & Sessions and are user-revocable

First-Use Provisioning (one-time per user)

MCP Client                    MCP Server                   Nextcloud
    │                             │                            │
    │── Bearer Token + request ──▶│                            │
    │                             │   No stored app password   │
    │                             │                            │
    │◀── Elicit URL or 401 ───────│                            │
    │   "Visit <login-url>"       │                            │
    │                             │── POST /index.php/login/v2▶│
    │                             │◀── login_url, poll_token ──│
    │                             │                            │
    │   User opens login_url in browser, authenticates, "Grant"│
    │   ──────────────────────────────────────────────────────▶│
    │                             │                            │
    │                             │── Poll endpoint (bg) ─────▶│
    │                             │◀── loginName, appPassword ─│
    │                             │                            │
    │                             │── Encrypt + store          │
    │                             │   in tokens.db             │
    │                             │                            │
    │── Retry request ───────────▶│── Basic Auth as above ────▶│

Background Sync

Uses the same per-user app password retrieved from encrypted storage. No token refresh needed — Nextcloud app passwords don't expire (until the user revokes them).

                              MCP Server                   Nextcloud
                                  │                            │
    [Background job starts]       │                            │
                                  │── Retrieve app password ──▶│
                                  │   (per user, from SQLite)  │
                                  │                            │
                                  │── HTTP + BasicAuth ───────▶│
                                  │◀── API Response ───────────│

Astrolabe → MCP Server

Same as Multi-User BasicAuth — see Astrolabe → MCP Server above.

Configuration Quick Reference

Single-User BasicAuth

NEXTCLOUD_HOST=https://nextcloud.example.com
NEXTCLOUD_USERNAME=admin
NEXTCLOUD_PASSWORD=<app-password>

Multi-User BasicAuth

NEXTCLOUD_HOST=https://nextcloud.example.com
ENABLE_MULTI_USER_BASIC_AUTH=true

# Optional: app-password storage for background sync
TOKEN_ENCRYPTION_KEY=<fernet-key>
TOKEN_STORAGE_DB=/app/data/tokens.db

Login Flow v2

NEXTCLOUD_HOST=https://nextcloud.example.com
ENABLE_LOGIN_FLOW=true

# Required for app-password storage
TOKEN_ENCRYPTION_KEY=<fernet-key>
TOKEN_STORAGE_DB=/app/data/tokens.db

# Public URLs (for browser redirects)
NEXTCLOUD_MCP_SERVER_URL=https://mcp.example.com
NEXTCLOUD_PUBLIC_ISSUER_URL=https://nextcloud.example.com

See Login Flow v2 for full setup, scope reference, and troubleshooting.

Related Documentation

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