dorfteich/docs/architecture/adr/0021-external-authentication.md
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docs: VS-NfD readiness planning (ist-aufnahme, plan, ADRs 0019-0026, issue drafts)
Add docs/vs-nfd/: the analysis brief, the as-is assessment (42 findings,
all verified against the code), the prioritized action plan rev. 2 with
issue references written back to every checkbox, the two-stage issue/ADR
brief, and the full reviewed draft used to create the forge state.

Add eight proposed ADRs 0019-0026 covering the VS-NfD architecture
decisions: no security base functions (par. 52 VSA anchor), HKDF token
key separation, external authentication, page classification, read-access
audit trail (variant A), reproducible offline deployment, plugin trust
model, and backup target restriction.

Forge state created alongside this commit: 11 labels, milestones M24-M31,
issues #188-#236 (docs-only change, no code touched).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0168Ph5uBmHm8X28CSVpbpnJ
2026-07-30 01:48:05 +02:00

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Markdown

# ADR 0021: External authentication via OIDC; local passwords optional
- Status: proposed
- Date: 2026-07-29
## Context
ADR 0007 established sessions and identities with OIDC in mind:
`UserIdentity.provider` is documented as `"password"` today and
`"oidc:<issuer>"` later, with `@@unique([provider, subject])` already in
place. No OIDC code exists — the readiness is structural only.
Authentication is a security base function under §52 VSA (ADR 0019), so it
belongs to the operator's platform. An authority environment additionally
brings its own account lifecycle: joiners, movers and leavers are managed
in the IdP, and a second account store inside the application would drift
from it.
Some environments terminate authentication at the perimeter instead and
expect the application to trust a header or a client certificate.
## Decision
1. **OIDC Authorization Code with PKCE is the primary path**, configured by
discovery, validated against JWKS. Keycloak is the reference IdP we
verify against; nothing in the implementation is Keycloak-specific.
2. **Identities use the existing slot**: `provider = "oidc:<issuer>"`,
`subject` from the token. Linking an OIDC identity to an existing local
user follows an explicit, documented rule — never silently by e-mail
address, which would be an account-takeover path.
3. **Local authentication is switchable off in full**, via
`auth.local.enabled = false`. "In full" means every credential-issuing
flow: password login, self-service signup, password reset,
verification-as-login, and the token flows (PAT, feed tokens). A
half-closed local path makes the operating concept untrue, which is
worse than not closing it.
4. **Proxy header and mTLS are a supported alternative path, off by
default.** When enabled they require an allowlist of trusted peers; a
request carrying the header from an untrusted peer is rejected and
audited. The trust boundary is stated explicitly in the security
documentation.
5. **Claims map onto the existing permission model** declaratively, and
mapped grants are written through the same service path as manual ones
so the permission cache stays correct. The application gains no second
authorization model.
6. **No MFA, no password policy engine of our own** (ADR 0019). Both are
the IdP's.
## Consequences
- Bootstrapping needs a documented answer: the first-run wizard creates a
local admin, so either it stays exempt with a stated compensating
control, or setup itself runs against the IdP. The choice is recorded in
#216.
- Whether the switch is deploy-level or runtime matters: a runtime setting
can be flipped back by a compromised Site-Admin. If it stays runtime,
that residual risk goes into #231.
- Existing password hashes remain in the database after the switch. Their
deletion is out of scope and, being Argon2id, they are not a
confidentiality problem — but the fact is documented.
- Session handling is unchanged: OIDC produces a session through the same
service, so there is exactly one session mechanism (see #190 for its
bounds).
- SAML and LDAP stay out. OIDC plus proxy/mTLS covers the environments we
target; adding SAML would be a new decision.
## Implementing issues
#214 (OIDC + PKCE), #215 (proxy header / mTLS), #216
(`auth.local.enabled`), #217 (claim mapping). Depends on #188 for the
vetted JWT implementation.