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refactor(oidc): drop single-subject allowlist, authenticate-only (ADR-012)

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ADR-011's single-user authz (ID-token subject must equal AllowedSubject,
else 403) is replaced by ADR-012's model: Dex authentication is the only
gate — any Dex-authenticated subject may establish a session. Whether that
subject has a tapir user, and routing to registration if not, is decided
downstream in internal/web (next commit).

Removals (noted): oidc.Config.AllowedSubject + its required-field check + the
callback 403 branch; config.Config.AllowedSubject + TAPIR_ALLOWED_SUBJECT env
wiring; the AllowedSubject arg in cmdServe. ui-spec.md updated to reflect the
supersession. Sessions, cookie signing, login/callback/logout unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
mathias
2026-06-03 15:56:13 +02:00
co-authored by Claude Opus 4.8
parent f396e01243
commit e62df0027d
5 changed files with 64 additions and 65 deletions
Download Patch File Download Diff File Expand all files Collapse all files
internal/web/oidc/oidc.go
+17 -24
View File
@@ -4,11 +4,13 @@
// interface, so swapping the stub for Dex is a wiring choice in cmd/tapir, not
// a code change (ADR-003).
//
// Authentication is real (Dex OIDC); authorization is single-user — the ID
// token's subject must equal Config.AllowedSubject or the request is refused
// with 403. Sessions are server-side (in-memory, fine for the single Stage-0
// replica) addressed by an HMAC-signed (HS256) HttpOnly Secure SameSite=Lax
// cookie with a short TTL and sliding refresh. Tokens are never logged.
// Authentication is real (Dex OIDC) and is the only gate: any Dex-authenticated
// subject may sign in (ADR-012 dropped ADR-011's single-subject allowlist).
// Authorization/registration is layered on top in internal/web (an authenticated
// subject with no tapir user is routed to registration). Sessions are server-side
// (in-memory, fine for the single Stage-1 replica) addressed by an HMAC-signed
// (HS256) HttpOnly Secure SameSite=Lax cookie with a short TTL and sliding
// refresh. Tokens are never logged.
//
// This is mcp-chassis's cousin but NOT the same code: mcp-chassis validates
// inbound Bearer JWTs for MCP APIs; this is a browser session login.
@@ -28,8 +30,8 @@ import (
)
// Config is the OIDC + session configuration. cmd/tapir maps these from
// TAPIR_OIDC_*/TAPIR_DEX_*/TAPIR_SESSION_SECRET/TAPIR_ALLOWED_SUBJECT; this
// package takes the resolved struct.
// TAPIR_OIDC_*/TAPIR_DEX_*/TAPIR_SESSION_SECRET; this package takes the resolved
// struct.
type Config struct {
// Issuer is the Dex issuer URL, e.g. https://auth.d-ma.be. Discovery
// (.well-known/openid-configuration) runs against it in New.
@@ -42,9 +44,6 @@ type Config struct {
RedirectURL string
// SessionSecret keys the HS256 session-cookie signature. Never logged.
SessionSecret string
// AllowedSubject is the single Dex subject permitted to sign in. Everyone
// else is refused 403 (single-user authz, ADR-011).
AllowedSubject string
}
const (
@@ -102,12 +101,11 @@ func WithInsecureCookies() Option {
// discovery request only.
func New(ctx context.Context, cfg Config, opts ...Option) (*DexAuth, error) {
for name, val := range map[string]string{
"issuer": cfg.Issuer,
"client id": cfg.ClientID,
"client secret": cfg.ClientSecret,
"redirect url": cfg.RedirectURL,
"session secret": cfg.SessionSecret,
"allowed subject": cfg.AllowedSubject,
"issuer": cfg.Issuer,
"client id": cfg.ClientID,
"client secret": cfg.ClientSecret,
"redirect url": cfg.RedirectURL,
"session secret": cfg.SessionSecret,
} {
if strings.TrimSpace(val) == "" {
return nil, fmt.Errorf("oidc: missing %s", name)
@@ -242,14 +240,9 @@ func (d *DexAuth) handleCallback(w http.ResponseWriter, r *http.Request) {
return
}
// Single-user authz: only the allowlisted subject may sign in. On mismatch
// we echo the caller's own subject (an opaque id, not a secret) so the
// maintainer can bootstrap TAPIR_ALLOWED_SUBJECT on first login.
if idToken.Subject != d.cfg.AllowedSubject {
http.Error(w, "forbidden — not the allowlisted subject. your subject is: "+idToken.Subject, http.StatusForbidden)
return
}
// Authentication is the only gate (ADR-012): any Dex-authenticated subject may
// establish a session. Whether that subject has a tapir user — and routing to
// registration if not — is decided downstream in internal/web, not here.
var claims struct {
Email string `json:"email"`
}
internal/web/oidc/oidc_test.go
+29 -22
View File
@@ -20,7 +20,7 @@ import (
const (
testClientID = "tapir-web"
allowedSub = "allowed-subject-123"
testSubject = "dex-subject-123"
)
// fakeIssuer is an httptest-backed OIDC provider: it serves a discovery
@@ -115,12 +115,11 @@ func writeJSON(t *testing.T, w http.ResponseWriter, v any) {
func newAuth(t *testing.T, f *fakeIssuer) *oidc.DexAuth {
t.Helper()
auth, err := oidc.New(context.Background(), oidc.Config{
Issuer: f.server.URL,
ClientID: testClientID,
ClientSecret: "test-client-secret",
RedirectURL: "http://tapir.test/auth/callback",
SessionSecret: "test-session-secret-please-change",
AllowedSubject: allowedSub,
Issuer: f.server.URL,
ClientID: testClientID,
ClientSecret: "test-client-secret",
RedirectURL: "http://tapir.test/auth/callback",
SessionSecret: "test-session-secret-please-change",
}, oidc.WithInsecureCookies())
require.NoError(t, err)
return auth
@@ -140,12 +139,12 @@ func login(t *testing.T, auth *oidc.DexAuth) (state, nonce string) {
return q.Get("state"), q.Get("nonce")
}
// authenticate completes a full login+callback for the allowlisted subject and
// returns the resulting session cookie.
// authenticate completes a full login+callback for the test subject and returns
// the resulting session cookie.
func authenticate(t *testing.T, auth *oidc.DexAuth, f *fakeIssuer) *http.Cookie {
t.Helper()
state, nonce := login(t, auth)
f.sub, f.email, f.nonce = allowedSub, "maintainer@d-ma.be", nonce
f.sub, f.email, f.nonce = testSubject, "maintainer@d-ma.be", nonce
rec := httptest.NewRecorder()
auth.Routes().ServeHTTP(rec, httptest.NewRequest(http.MethodGet,
@@ -189,7 +188,7 @@ func TestLoginRedirectsToAuthorize(t *testing.T) {
require.Contains(t, q.Get("scope"), "openid")
}
func TestCallbackAllowedSubjectSetsSession(t *testing.T) {
func TestCallbackSetsSession(t *testing.T) {
f := newFakeIssuer(t)
auth := newAuth(t, f)
@@ -199,26 +198,35 @@ func TestCallbackAllowedSubjectSetsSession(t *testing.T) {
req.AddCookie(cookie)
user, ok := auth.CurrentUser(req)
require.True(t, ok)
require.Equal(t, allowedSub, user.Subject)
require.Equal(t, testSubject, user.Subject)
require.Equal(t, "maintainer@d-ma.be", user.Email)
require.True(t, cookie.HttpOnly)
require.Equal(t, http.SameSiteLaxMode, cookie.SameSite)
}
func TestCallbackNonAllowedSubjectForbidden(t *testing.T) {
// TestCallbackAnySubjectAuthenticates proves the single-subject allowlist is gone
// (ADR-012): a subject other than any prior allowlist still gets a session.
func TestCallbackAnySubjectAuthenticates(t *testing.T) {
f := newFakeIssuer(t)
auth := newAuth(t, f)
state, nonce := login(t, auth)
f.sub, f.email, f.nonce = "intruder-999", "intruder@elsewhere.test", nonce
f.sub, f.email, f.nonce = "some-other-subject-999", "other@elsewhere.test", nonce
rec := httptest.NewRecorder()
auth.Routes().ServeHTTP(rec, httptest.NewRequest(http.MethodGet,
"/auth/callback?code=valid-code&state="+state, nil))
require.Equal(t, http.StatusForbidden, rec.Code)
require.Empty(t, rec.Result().Cookies(), "no session for a rejected subject")
require.Equal(t, http.StatusFound, rec.Code)
require.Equal(t, "/", rec.Header().Get("Location"))
cookie := sessionCookie(t, rec.Result())
req := httptest.NewRequest(http.MethodGet, "/", nil)
req.AddCookie(cookie)
user, ok := auth.CurrentUser(req)
require.True(t, ok)
require.Equal(t, "some-other-subject-999", user.Subject)
}
func TestCallbackUnknownStateRejected(t *testing.T) {
@@ -304,12 +312,11 @@ func TestExpiredSessionRejected(t *testing.T) {
f := newFakeIssuer(t)
clock := time.Now()
auth, err := oidc.New(context.Background(), oidc.Config{
Issuer: f.server.URL,
ClientID: testClientID,
ClientSecret: "test-client-secret",
RedirectURL: "http://tapir.test/auth/callback",
SessionSecret: "test-session-secret-please-change",
AllowedSubject: allowedSub,
Issuer: f.server.URL,
ClientID: testClientID,
ClientSecret: "test-client-secret",
RedirectURL: "http://tapir.test/auth/callback",
SessionSecret: "test-session-secret-please-change",
}, oidc.WithInsecureCookies(),
oidc.WithSessionTTL(time.Minute),
oidc.WithClock(func() time.Time { return clock }))