feat(master): OIDC login with group check, sessions and CSRF protection

go.mod

@@ -4,11 +4,13 @@ go 1.26.3
 
 require (
 	github.com/coder/websocket v1.8.15
+	github.com/coreos/go-oidc/v3 v3.21.0
 	github.com/docker/docker v28.5.2+incompatible
 	github.com/jackc/pgx/v5 v5.10.0
 	github.com/prometheus/client_golang v1.23.2
 	github.com/prometheus/client_model v0.6.2
 	github.com/stretchr/testify v1.11.1
+	golang.org/x/oauth2 v0.36.0
 )
 
 require (
@@ -23,6 +25,7 @@ require (
 	github.com/docker/go-connections v0.7.0 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect

go.sum

@@ -16,6 +16,8 @@ github.com/containerd/errdefs/pkg v0.3.0 h1:9IKJ06FvyNlexW690DXuQNx2KA2cUJXx151X
 github.com/containerd/errdefs/pkg v0.3.0/go.mod h1:NJw6s9HwNuRhnjJhM7pylWwMyAkmCQvQ4GpJHEqRLVk=
 github.com/containerd/log v0.1.0 h1:TCJt7ioM2cr/tfR8GPbGf9/VRAX8D2B4PjzCpfX540I=
 github.com/containerd/log v0.1.0/go.mod h1:VRRf09a7mHDIRezVKTRCrOq78v577GXq3bSa3EhrzVo=
+github.com/coreos/go-oidc/v3 v3.21.0 h1:wZo4Q9Pum8dYEj0eMUPrqR+kvuGkeUplbLpNCkBqoWM=
+github.com/coreos/go-oidc/v3 v3.21.0/go.mod h1:DYCf24+ncYi+XkIH97GY1+dqoRlbaSI26KVTCI9SrY4=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -29,6 +31,8 @@ github.com/docker/go-units v0.5.0 h1:69rxXcBk27SvSaaxTtLh/8llcHD8vYHT7WSdRZ/jvr4
 github.com/docker/go-units v0.5.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
 github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
 github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
+github.com/go-jose/go-jose/v4 v4.1.4 h1:moDMcTHmvE6Groj34emNPLs/qtYXRVcd6S7NHbHz3kA=
+github.com/go-jose/go-jose/v4 v4.1.4/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
 github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
 github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
@@ -119,6 +123,8 @@ go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
 go.yaml.in/yaml/v2 v2.4.2/go.mod h1:081UH+NErpNdqlCXm3TtEran0rJZGxAYx9hb/ELlsPU=
 golang.org/x/net v0.52.0 h1:He/TN1l0e4mmR3QqHMT2Xab3Aj3L9qjbhRm78/6jrW0=
 golang.org/x/net v0.52.0/go.mod h1:R1MAz7uMZxVMualyPXb+VaqGSa3LIaUqk0eEt3w36Sw=
+golang.org/x/oauth2 v0.36.0 h1:peZ/1z27fi9hUOFCAZaHyrpWG5lwe0RJEEEeH0ThlIs=
+golang.org/x/oauth2 v0.36.0/go.mod h1:YDBUJMTkDnJS+A4BP4eZBjCqtokkg1hODuPjwiGPO7Q=
 golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
 golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=

internal/master/webauth/auth.go

@@ -0,0 +1,184 @@
+// Package webauth logs people into the master UI through OIDC (Authentik),
+// keeps their sessions, and protects state-changing requests with a CSRF
+// token.
+package webauth
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"errors"
+	"log/slog"
+	"net/http"
+	"slices"
+	"strings"
+	"time"
+
+	"golang.org/x/oauth2"
+
+	"github.com/shcizo/package-updater/internal/master/model"
+)
+
+const (
+	sessionCookieName = "pu_session"
+	flowCookieName    = "pu_oidc_flow"
+	sessionTTL        = 12 * time.Hour
+)
+
+// Store keeps sessions. *store.Store satisfies it.
+type Store interface {
+	CreateSession(ctx context.Context, s model.Session) error
+	GetSession(ctx context.Context, id string, now time.Time) (model.Session, error)
+	DeleteSession(ctx context.Context, id string) error
+}
+
+// Auth holds the login handlers and the session middleware.
+type Auth struct {
+	provider     Provider
+	store        Store
+	allowedGroup string
+	secure       bool
+	log          *slog.Logger
+	now          func() time.Time
+}
+
+// New returns an Auth. Only members of allowedGroup may log in. secureCookies
+// should be true whenever the UI is served over HTTPS.
+func New(p Provider, s Store, allowedGroup string, secureCookies bool, log *slog.Logger) *Auth {
+	return &Auth{provider: p, store: s, allowedGroup: allowedGroup, secure: secureCookies, log: log, now: time.Now}
+}
+
+// Login starts the OIDC flow. State and PKCE verifier travel in a short-lived
+// cookie scoped to /auth/; tampering with it can only break the user's own
+// login.
+func (a *Auth) Login(w http.ResponseWriter, r *http.Request) {
+	state := randomString()
+	verifier := oauth2.GenerateVerifier()
+	http.SetCookie(w, &http.Cookie{
+		Name: flowCookieName, Value: state + "." + verifier, Path: "/auth/",
+		MaxAge: 600, HttpOnly: true, Secure: a.secure, SameSite: http.SameSiteLaxMode,
+	})
+	http.Redirect(w, r, a.provider.AuthCodeURL(state, verifier), http.StatusFound)
+}
+
+// Callback finishes the OIDC flow, checks group membership and creates the
+// session.
+func (a *Auth) Callback(w http.ResponseWriter, r *http.Request) {
+	flow, err := r.Cookie(flowCookieName)
+	if err != nil {
+		http.Error(w, "login flow expired, start again", http.StatusBadRequest)
+		return
+	}
+	state, verifier, ok := strings.Cut(flow.Value, ".")
+	if !ok || subtle.ConstantTimeCompare([]byte(r.URL.Query().Get("state")), []byte(state)) != 1 {
+		http.Error(w, "invalid login state", http.StatusBadRequest)
+		return
+	}
+	http.SetCookie(w, &http.Cookie{Name: flowCookieName, Path: "/auth/", MaxAge: -1})
+
+	claims, err := a.provider.Exchange(r.Context(), r.URL.Query().Get("code"), verifier)
+	if err != nil {
+		a.log.Warn("login_failed", "error", err)
+		http.Error(w, "login failed", http.StatusUnauthorized)
+		return
+	}
+	if !slices.Contains(claims.Groups, a.allowedGroup) {
+		a.log.Warn("login_forbidden", "subject", claims.Subject, "required_group", a.allowedGroup)
+		http.Error(w, "forbidden: you are not a member of the group allowed to use package-updater", http.StatusForbidden)
+		return
+	}
+
+	sess := model.Session{
+		ID: randomString(), Subject: claims.Subject, Name: claims.Name, Email: claims.Email,
+		CSRFToken: randomString(), ExpiresAt: a.now().Add(sessionTTL),
+	}
+	if err := a.store.CreateSession(r.Context(), sess); err != nil {
+		a.log.Error("create_session_failed", "error", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	http.SetCookie(w, &http.Cookie{
+		Name: sessionCookieName, Value: sess.ID, Path: "/", Expires: sess.ExpiresAt,
+		HttpOnly: true, Secure: a.secure, SameSite: http.SameSiteLaxMode,
+	})
+	a.log.Info("login", "subject", claims.Subject, "name", claims.Name)
+	http.Redirect(w, r, "/", http.StatusFound)
+}
+
+// Logout ends the session. Mount behind Require so it is CSRF-protected.
+func (a *Auth) Logout(w http.ResponseWriter, r *http.Request) {
+	if s, ok := SessionFrom(r.Context()); ok {
+		if err := a.store.DeleteSession(r.Context(), s.ID); err != nil {
+			a.log.Error("delete_session_failed", "error", err)
+		}
+	}
+	http.SetCookie(w, &http.Cookie{Name: sessionCookieName, Path: "/", MaxAge: -1})
+	_, _ = w.Write([]byte("Logged out."))
+}
+
+// Require lets a request through only with a valid session, and for
+// anything but GET/HEAD only with the session's CSRF token in the
+// X-CSRF-Token header or the csrf_token form field. htmx requests without a
+// session get 401 + HX-Redirect so the whole page navigates to the login,
+// instead of the login page being swapped into a fragment. Event-stream
+// (SSE) requests without a session get a plain 401: a redirect would make
+// the browser's EventSource retry /auth/login repeatedly and overwrite the
+// login flow cookie of a login in progress in another tab.
+func (a *Auth) Require(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		sess, err := a.session(r)
+		if err != nil && !errors.Is(err, model.ErrNotFound) {
+			a.log.Error("session_lookup_failed", "error", err)
+			http.Error(w, "internal error", http.StatusInternalServerError)
+			return
+		}
+		if err != nil {
+			switch {
+			case r.Header.Get("HX-Request") == "true":
+				w.Header().Set("HX-Redirect", "/auth/login")
+				w.WriteHeader(http.StatusUnauthorized)
+			case strings.Contains(r.Header.Get("Accept"), "text/event-stream"):
+				w.WriteHeader(http.StatusUnauthorized)
+			case r.Method == http.MethodGet:
+				http.Redirect(w, r, "/auth/login", http.StatusFound)
+			default:
+				http.Error(w, "unauthorized", http.StatusUnauthorized)
+			}
+			return
+		}
+		if r.Method != http.MethodGet && r.Method != http.MethodHead {
+			token := r.Header.Get("X-CSRF-Token")
+			if token == "" {
+				token = r.FormValue("csrf_token")
+			}
+			if subtle.ConstantTimeCompare([]byte(token), []byte(sess.CSRFToken)) != 1 {
+				http.Error(w, "invalid CSRF token", http.StatusForbidden)
+				return
+			}
+		}
+		next.ServeHTTP(w, r.WithContext(context.WithValue(r.Context(), sessionKey{}, sess)))
+	})
+}
+
+func (a *Auth) session(r *http.Request) (model.Session, error) {
+	c, err := r.Cookie(sessionCookieName)
+	if err != nil {
+		return model.Session{}, model.ErrNotFound
+	}
+	return a.store.GetSession(r.Context(), c.Value, a.now())
+}
+
+type sessionKey struct{}
+
+// SessionFrom returns the session Require stored in ctx.
+func SessionFrom(ctx context.Context) (model.Session, bool) {
+	s, ok := ctx.Value(sessionKey{}).(model.Session)
+	return s, ok
+}
+
+func randomString() string {
+	var b [32]byte
+	_, _ = rand.Read(b[:])
+	return base64.RawURLEncoding.EncodeToString(b[:])
+}

internal/master/webauth/auth_test.go

@@ -0,0 +1,227 @@
+package webauth
+
+import (
+	"context"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/shcizo/package-updater/internal/master/model"
+)
+
+type fakeProvider struct {
+	claims Claims
+	err    error
+	gotVer string
+}
+
+func (p *fakeProvider) AuthCodeURL(state, _ string) string {
+	return "https://auth.example/authorize?state=" + url.QueryEscape(state)
+}
+
+func (p *fakeProvider) Exchange(_ context.Context, _ string, verifier string) (Claims, error) {
+	p.gotVer = verifier
+	return p.claims, p.err
+}
+
+type fakeStore struct {
+	mu       sync.Mutex
+	sessions map[string]model.Session
+}
+
+func newFakeStore() *fakeStore { return &fakeStore{sessions: map[string]model.Session{}} }
+
+func (f *fakeStore) CreateSession(_ context.Context, s model.Session) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.sessions[s.ID] = s
+	return nil
+}
+
+func (f *fakeStore) GetSession(_ context.Context, id string, now time.Time) (model.Session, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	s, ok := f.sessions[id]
+	if !ok || !s.ExpiresAt.After(now) {
+		return model.Session{}, model.ErrNotFound
+	}
+	return s, nil
+}
+
+func (f *fakeStore) DeleteSession(_ context.Context, id string) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	delete(f.sessions, id)
+	return nil
+}
+
+func newAuth(p *fakeProvider, s *fakeStore) *Auth {
+	return New(p, s, "updater-admins", true, slog.New(slog.NewTextHandler(io.Discard, nil)))
+}
+
+// startLogin runs /auth/login and returns the flow cookie and the state.
+func startLogin(t *testing.T, a *Auth) (*http.Cookie, string) {
+	t.Helper()
+	rec := httptest.NewRecorder()
+	a.Login(rec, httptest.NewRequest(http.MethodGet, "/auth/login", nil))
+	require.Equal(t, http.StatusFound, rec.Code)
+	loc, err := url.Parse(rec.Header().Get("Location"))
+	require.NoError(t, err)
+	cookies := rec.Result().Cookies()
+	require.Len(t, cookies, 1)
+	return cookies[0], loc.Query().Get("state")
+}
+
+func callback(a *Auth, flow *http.Cookie, state string) *httptest.ResponseRecorder {
+	req := httptest.NewRequest(http.MethodGet, "/auth/callback?code=c&state="+url.QueryEscape(state), nil)
+	req.AddCookie(flow)
+	rec := httptest.NewRecorder()
+	a.Callback(rec, req)
+	return rec
+}
+
+func TestLogin_SetsFlowCookieAndRedirects(t *testing.T) {
+	a := newAuth(&fakeProvider{}, newFakeStore())
+	flow, state := startLogin(t, a)
+	assert.True(t, flow.HttpOnly)
+	assert.True(t, flow.Secure)
+	assert.NotEmpty(t, state)
+}
+
+func TestCallback_StateMismatchRejected(t *testing.T) {
+	a := newAuth(&fakeProvider{}, newFakeStore())
+	flow, _ := startLogin(t, a)
+	rec := callback(a, flow, "forged")
+	assert.Equal(t, http.StatusBadRequest, rec.Code)
+}
+
+func TestCallback_UserOutsideGroupForbidden(t *testing.T) {
+	store := newFakeStore()
+	a := newAuth(&fakeProvider{claims: Claims{Subject: "u", Groups: []string{"family"}}}, store)
+	flow, state := startLogin(t, a)
+	rec := callback(a, flow, state)
+	assert.Equal(t, http.StatusForbidden, rec.Code)
+	assert.Empty(t, store.sessions)
+}
+
+func TestCallback_ExchangeFailure(t *testing.T) {
+	a := newAuth(&fakeProvider{err: errors.New("bad code")}, newFakeStore())
+	flow, state := startLogin(t, a)
+	assert.Equal(t, http.StatusUnauthorized, callback(a, flow, state).Code)
+}
+
+func TestCallback_CreatesSession(t *testing.T) {
+	store := newFakeStore()
+	p := &fakeProvider{claims: Claims{Subject: "u1", Name: "Samuel", Groups: []string{"updater-admins"}}}
+	a := newAuth(p, store)
+	flow, state := startLogin(t, a)
+	rec := callback(a, flow, state)
+
+	require.Equal(t, http.StatusFound, rec.Code)
+	assert.Equal(t, "/", rec.Header().Get("Location"))
+	assert.NotEmpty(t, p.gotVer, "the PKCE verifier from the flow cookie must reach the exchange")
+	var sessionCookie *http.Cookie
+	for _, c := range rec.Result().Cookies() {
+		if c.Name == sessionCookieName {
+			sessionCookie = c
+		}
+	}
+	require.NotNil(t, sessionCookie)
+	assert.True(t, sessionCookie.HttpOnly)
+	assert.Equal(t, http.SameSiteLaxMode, sessionCookie.SameSite)
+	s, ok := store.sessions[sessionCookie.Value]
+	require.True(t, ok)
+	assert.Equal(t, "Samuel", s.Name)
+	assert.NotEmpty(t, s.CSRFToken)
+}
+
+func protectedRequest(method, target string, sessionID string) *http.Request {
+	req := httptest.NewRequest(method, target, nil)
+	if sessionID != "" {
+		req.AddCookie(&http.Cookie{Name: sessionCookieName, Value: sessionID})
+	}
+	return req
+}
+
+func TestRequire(t *testing.T) {
+	store := newFakeStore()
+	store.sessions["live"] = model.Session{ID: "live", Name: "Samuel", CSRFToken: "tok", ExpiresAt: time.Now().Add(time.Hour)}
+	store.sessions["old"] = model.Session{ID: "old", CSRFToken: "tok", ExpiresAt: time.Now().Add(-time.Hour)}
+	a := newAuth(&fakeProvider{}, store)
+
+	var gotName string
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		s, _ := SessionFrom(r.Context())
+		gotName = s.Name
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h := a.Require(next)
+
+	cases := []struct {
+		name       string
+		req        *http.Request
+		wantCode   int
+		wantHeader [2]string
+	}{
+		{"no session GET redirects to login", protectedRequest(http.MethodGet, "/", ""), http.StatusFound, [2]string{"Location", "/auth/login"}},
+		{"expired session on htmx fragment", func() *http.Request {
+			r := protectedRequest(http.MethodGet, "/fragments/services", "old")
+			r.Header.Set("HX-Request", "true")
+			return r
+		}(), http.StatusUnauthorized, [2]string{"HX-Redirect", "/auth/login"}},
+		{"event-stream without session gets plain 401", func() *http.Request {
+			r := protectedRequest(http.MethodGet, "/events", "")
+			r.Header.Set("Accept", "text/event-stream")
+			return r
+		}(), http.StatusUnauthorized, [2]string{"Location", ""}},
+		{"no session POST", protectedRequest(http.MethodPost, "/agents", ""), http.StatusUnauthorized, [2]string{}},
+		{"POST without CSRF", protectedRequest(http.MethodPost, "/agents", "live"), http.StatusForbidden, [2]string{}},
+		{"POST with CSRF header", func() *http.Request {
+			r := protectedRequest(http.MethodPost, "/agents", "live")
+			r.Header.Set("X-CSRF-Token", "tok")
+			return r
+		}(), http.StatusNoContent, [2]string{}},
+		{"POST with CSRF form field", func() *http.Request {
+			r := httptest.NewRequest(http.MethodPost, "/agents", strings.NewReader("csrf_token=tok"))
+			r.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+			r.AddCookie(&http.Cookie{Name: sessionCookieName, Value: "live"})
+			return r
+		}(), http.StatusNoContent, [2]string{}},
+		{"GET with session", protectedRequest(http.MethodGet, "/", "live"), http.StatusNoContent, [2]string{}},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, c.req)
+			assert.Equal(t, c.wantCode, rec.Code)
+			if c.wantHeader[0] != "" {
+				assert.Equal(t, c.wantHeader[1], rec.Header().Get(c.wantHeader[0]))
+			}
+		})
+	}
+	assert.Equal(t, "Samuel", gotName)
+}
+
+func TestLogout_DeletesSession(t *testing.T) {
+	store := newFakeStore()
+	store.sessions["live"] = model.Session{ID: "live", CSRFToken: "tok", ExpiresAt: time.Now().Add(time.Hour)}
+	a := newAuth(&fakeProvider{}, store)
+
+	req := protectedRequest(http.MethodPost, "/auth/logout", "live")
+	req.Header.Set("X-CSRF-Token", "tok")
+	rec := httptest.NewRecorder()
+	a.Require(http.HandlerFunc(a.Logout)).ServeHTTP(rec, req)
+
+	assert.Equal(t, http.StatusOK, rec.Code)
+	assert.Empty(t, store.sessions)
+}

internal/master/webauth/provider.go

@@ -0,0 +1,85 @@
+package webauth
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/coreos/go-oidc/v3/oidc"
+	"golang.org/x/oauth2"
+)
+
+// Claims is what the master needs from the identity provider.
+type Claims struct {
+	Subject string
+	Name    string
+	Email   string
+	Groups  []string
+}
+
+// Provider performs the OIDC authorization code flow with PKCE. Declared as
+// an interface so handlers can be tested without a real identity provider.
+type Provider interface {
+	AuthCodeURL(state, verifier string) string
+	Exchange(ctx context.Context, code, verifier string) (Claims, error)
+}
+
+// OIDCConfig configures the real provider.
+type OIDCConfig struct {
+	Issuer       string // e.g. https://auth.example.com/application/o/package-updater/
+	ClientID     string
+	ClientSecret string
+	RedirectURL  string // PUBLIC_URL + /auth/callback
+}
+
+type oidcProvider struct {
+	oauth    *oauth2.Config
+	verifier *oidc.IDTokenVerifier
+}
+
+// NewOIDCProvider discovers the issuer's endpoints. It makes a network call,
+// so the master fails at startup if Authentik is unreachable.
+func NewOIDCProvider(ctx context.Context, cfg OIDCConfig) (Provider, error) {
+	p, err := oidc.NewProvider(ctx, cfg.Issuer)
+	if err != nil {
+		return nil, fmt.Errorf("oidc discovery: %w", err)
+	}
+	return &oidcProvider{
+		oauth: &oauth2.Config{
+			ClientID:     cfg.ClientID,
+			ClientSecret: cfg.ClientSecret,
+			Endpoint:     p.Endpoint(),
+			RedirectURL:  cfg.RedirectURL,
+			Scopes:       []string{oidc.ScopeOpenID, "profile", "email"},
+		},
+		verifier: p.Verifier(&oidc.Config{ClientID: cfg.ClientID}),
+	}, nil
+}
+
+func (p *oidcProvider) AuthCodeURL(state, verifier string) string {
+	return p.oauth.AuthCodeURL(state, oauth2.S256ChallengeOption(verifier))
+}
+
+func (p *oidcProvider) Exchange(ctx context.Context, code, verifier string) (Claims, error) {
+	tok, err := p.oauth.Exchange(ctx, code, oauth2.VerifierOption(verifier))
+	if err != nil {
+		return Claims{}, fmt.Errorf("exchange code: %w", err)
+	}
+	raw, ok := tok.Extra("id_token").(string)
+	if !ok {
+		return Claims{}, errors.New("token response has no id_token")
+	}
+	idt, err := p.verifier.Verify(ctx, raw)
+	if err != nil {
+		return Claims{}, fmt.Errorf("verify id_token: %w", err)
+	}
+	var c struct {
+		Name   string   `json:"name"`
+		Email  string   `json:"email"`
+		Groups []string `json:"groups"`
+	}
+	if err := idt.Claims(&c); err != nil {
+		return Claims{}, fmt.Errorf("read claims: %w", err)
+	}
+	return Claims{Subject: idt.Subject, Name: c.Name, Email: c.Email, Groups: c.Groups}, nil
+}