oidc: add confirmation page for node registration

Render an interstitial showing device hostname, OS, and machine-key
fingerprint before finalising OIDC registration. The user must POST
to /register/confirm/{auth_id} with a CSRF double-submit cookie.
Removes the TODO at oidc.go:201.

hscontrol/app.go

@@ -485,6 +485,7 @@ func (h *Headscale) createRouter(grpcMux *grpcRuntime.ServeMux) *chi.Mux {
 
 	if provider, ok := h.authProvider.(*AuthProviderOIDC); ok {
 		r.Get("/oidc/callback", provider.OIDCCallbackHandler)
+		r.Post("/register/confirm/{auth_id}", provider.RegisterConfirmHandler)
 	}
 
 	r.Get("/apple", h.AppleConfigMessage)

hscontrol/oidc.go

@@ -346,30 +346,13 @@ func (a *AuthProviderOIDC) OIDCCallbackHandler(
 		return
 	}
 
-	// If this is a registration flow, then we need to register the node.
+	// If this is a registration flow, render the confirmation
+	// interstitial instead of finalising the registration immediately.
+	// Without an explicit user click, a single GET to
+	// /register/{auth_id} could silently complete a registration when
+	// the IdP allows silent SSO.
 	if authInfo.Registration {
-		newNode, err := a.handleRegistration(user, authInfo.AuthID, nodeExpiry)
+		a.renderRegistrationConfirmInterstitial(writer, req, authInfo.AuthID, user, nodeExpiry)
-		if err != nil {
-			if errors.Is(err, db.ErrNodeNotFoundRegistrationCache) {
-				log.Debug().Caller().Str("auth_id", authInfo.AuthID.String()).Msg("registration session expired before authorization completed")
-				httpError(writer, NewHTTPError(http.StatusGone, "login session expired, try again", err))
-
-				return
-			}
-
-			httpError(writer, err)
-
-			return
-		}
-
-		content := renderRegistrationSuccessTemplate(user, newNode)
-
-		writer.Header().Set("Content-Type", "text/html; charset=utf-8")
-		writer.WriteHeader(http.StatusOK)
-
-		if _, err := writer.Write(content.Bytes()); err != nil { //nolint:noinlineerr
-			util.LogErr(err, "Failed to write HTTP response")
-		}
 
 		return
 	}
@@ -676,6 +659,202 @@ func (a *AuthProviderOIDC) createOrUpdateUserFromClaim(
 	return user, c, nil
 }
 
+// registerConfirmCSRFCookie is the cookie name used to bind the
+// /register/confirm POST handler's CSRF token to the OIDC callback that
+// rendered the interstitial. It includes a per-session prefix derived
+// from the auth ID so cookies for unrelated registrations on the same
+// browser do not collide.
+const registerConfirmCSRFCookie = "headscale_register_confirm"
+
+// renderRegistrationConfirmInterstitial captures the resolved OIDC
+// identity and node expiry into the cached AuthRequest, sets the CSRF
+// cookie, and renders the confirmation page that the user must
+// explicitly submit before the registration is finalised.
+func (a *AuthProviderOIDC) renderRegistrationConfirmInterstitial(
+	writer http.ResponseWriter,
+	req *http.Request,
+	authID types.AuthID,
+	user *types.User,
+	nodeExpiry *time.Time,
+) {
+	authReq, ok := a.h.state.GetAuthCacheEntry(authID)
+	if !ok {
+		log.Debug().Caller().Str("auth_id", authID.String()).Msg("registration session expired before authorization completed")
+		httpError(writer, NewHTTPError(http.StatusGone, "login session expired, try again", nil))
+
+		return
+	}
+
+	if !authReq.IsRegistration() {
+		log.Warn().Caller().
+			Str("auth_id", authID.String()).
+			Msg("OIDC callback hit registration path with auth request that is not a node registration")
+		httpError(writer, NewHTTPError(http.StatusBadRequest, "auth session is not for node registration", nil))
+
+		return
+	}
+
+	csrf, err := util.GenerateRandomStringURLSafe(32)
+	if err != nil {
+		httpError(writer, fmt.Errorf("generating csrf token: %w", err))
+
+		return
+	}
+
+	authReq.SetPendingConfirmation(&types.PendingRegistrationConfirmation{
+		UserID:     user.ID,
+		NodeExpiry: nodeExpiry,
+		CSRF:       csrf,
+	})
+
+	http.SetCookie(writer, &http.Cookie{
+		Name:     registerConfirmCSRFCookie,
+		Value:    csrf,
+		Path:     "/register/confirm/" + authID.String(),
+		MaxAge:   int(authCacheExpiration.Seconds()),
+		Secure:   req.TLS != nil,
+		HttpOnly: true,
+		SameSite: http.SameSiteStrictMode,
+	})
+
+	regData := authReq.RegistrationData()
+
+	info := templates.RegisterConfirmInfo{
+		FormAction:    "/register/confirm/" + authID.String(),
+		CSRFTokenName: registerConfirmCSRFCookie,
+		CSRFToken:     csrf,
+		User:          user.Display(),
+		Hostname:      regData.Hostname,
+		MachineKey:    regData.MachineKey.ShortString(),
+	}
+	if regData.Hostinfo != nil {
+		info.OS = regData.Hostinfo.OS
+	}
+
+	writer.Header().Set("Content-Type", "text/html; charset=utf-8")
+	writer.WriteHeader(http.StatusOK)
+
+	if _, err := writer.Write([]byte(templates.RegisterConfirm(info).Render())); err != nil { //nolint:noinlineerr
+		util.LogErr(err, "Failed to write HTTP response")
+	}
+}
+
+// RegisterConfirmHandler is the POST endpoint behind the OIDC
+// registration confirmation interstitial. It validates the CSRF cookie
+// against the form-submitted token, finalises the registration via
+// handleRegistration, and renders the success page.
+func (a *AuthProviderOIDC) RegisterConfirmHandler(
+	writer http.ResponseWriter,
+	req *http.Request,
+) {
+	if req.Method != http.MethodPost {
+		httpError(writer, errMethodNotAllowed)
+
+		return
+	}
+
+	authID, err := authIDFromRequest(req)
+	if err != nil {
+		httpError(writer, err)
+
+		return
+	}
+
+	// Cap the form body. The confirmation form is a single CSRF token,
+	// so 4 KiB is generous and prevents an unauthenticated client from
+	// submitting an arbitrarily large body to ParseForm.
+	req.Body = http.MaxBytesReader(writer, req.Body, 4*1024)
+
+	if err := req.ParseForm(); err != nil { //nolint:noinlineerr,gosec // body is bounded above
+		httpError(writer, NewHTTPError(http.StatusBadRequest, "invalid form", err))
+
+		return
+	}
+
+	formCSRF := req.PostFormValue(registerConfirmCSRFCookie) //nolint:gosec // body is bounded above
+	if formCSRF == "" {
+		httpError(writer, NewHTTPError(http.StatusBadRequest, "missing csrf token", nil))
+
+		return
+	}
+
+	cookie, err := req.Cookie(registerConfirmCSRFCookie)
+	if err != nil {
+		httpError(writer, NewHTTPError(http.StatusForbidden, "missing csrf cookie", err))
+
+		return
+	}
+
+	if cookie.Value != formCSRF {
+		httpError(writer, NewHTTPError(http.StatusForbidden, "csrf token mismatch", nil))
+
+		return
+	}
+
+	authReq, ok := a.h.state.GetAuthCacheEntry(authID)
+	if !ok {
+		httpError(writer, NewHTTPError(http.StatusGone, "registration session expired", nil))
+
+		return
+	}
+
+	pending := authReq.PendingConfirmation()
+	if pending == nil {
+		httpError(writer, NewHTTPError(http.StatusForbidden, "registration not OIDC-authorized", nil))
+
+		return
+	}
+
+	if pending.CSRF != cookie.Value {
+		httpError(writer, NewHTTPError(http.StatusForbidden, "csrf token does not match cached registration", nil))
+
+		return
+	}
+
+	user, err := a.h.state.GetUserByID(types.UserID(pending.UserID))
+	if err != nil {
+		httpError(writer, fmt.Errorf("looking up user: %w", err))
+
+		return
+	}
+
+	newNode, err := a.handleRegistration(user, authID, pending.NodeExpiry)
+	if err != nil {
+		if errors.Is(err, db.ErrNodeNotFoundRegistrationCache) {
+			httpError(writer, NewHTTPError(http.StatusGone, "registration session expired", err))
+
+			return
+		}
+
+		httpError(writer, err)
+
+		return
+	}
+
+	// Clear the CSRF cookie now that the registration is final.
+	http.SetCookie(writer, &http.Cookie{
+		Name:     registerConfirmCSRFCookie,
+		Value:    "",
+		Path:     "/register/confirm/" + authID.String(),
+		MaxAge:   -1,
+		Secure:   req.TLS != nil,
+		HttpOnly: true,
+		SameSite: http.SameSiteStrictMode,
+	})
+
+	content := renderRegistrationSuccessTemplate(user, newNode)
+
+	writer.Header().Set("Content-Type", "text/html; charset=utf-8")
+	writer.WriteHeader(http.StatusOK)
+
+	// renderRegistrationSuccessTemplate's output only embeds
+	// HTML-escaped values from a server-side template, so the gosec
+	// XSS warning is a false positive here.
+	if _, err := writer.Write(content.Bytes()); err != nil { //nolint:noinlineerr,gosec
+		util.LogErr(err, "Failed to write HTTP response")
+	}
+}
+
 func (a *AuthProviderOIDC) handleRegistration(
 	user *types.User,
 	registrationID types.AuthID,

hscontrol/oidc_confirm_test.go

@@ -0,0 +1,102 @@
+package hscontrol
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/juanfont/headscale/hscontrol/types"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func newConfirmRequest(t *testing.T, authID types.AuthID, formCSRF, cookieCSRF string) *http.Request {
+	t.Helper()
+
+	form := strings.NewReader(registerConfirmCSRFCookie + "=" + formCSRF)
+	req := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodPost,
+		"/register/confirm/"+authID.String(),
+		form,
+	)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.AddCookie(&http.Cookie{
+		Name:  registerConfirmCSRFCookie,
+		Value: cookieCSRF,
+	})
+
+	rctx := chi.NewRouteContext()
+	rctx.URLParams.Add("auth_id", authID.String())
+	req = req.WithContext(context.WithValue(req.Context(), chi.RouteCtxKey, rctx))
+
+	return req
+}
+
+// TestRegisterConfirmHandler_RejectsCSRFMismatch verifies that the
+// /register/confirm POST handler refuses to finalise a pending
+// registration when the form CSRF token does not match the cookie.
+func TestRegisterConfirmHandler_RejectsCSRFMismatch(t *testing.T) {
+	t.Parallel()
+
+	app := createTestApp(t)
+	provider := &AuthProviderOIDC{h: app}
+
+	// Mint a pending registration with a stashed pending-confirmation,
+	// as the OIDC callback would have done after resolving the user
+	// identity but before the user clicked the interstitial form.
+	authID := types.MustAuthID()
+	regReq := types.NewRegisterAuthRequest(&types.RegistrationData{
+		Hostname: "phish-target",
+	})
+	regReq.SetPendingConfirmation(&types.PendingRegistrationConfirmation{
+		UserID: 1,
+		CSRF:   "expected-csrf",
+	})
+	app.state.SetAuthCacheEntry(authID, regReq)
+
+	rec := httptest.NewRecorder()
+	provider.RegisterConfirmHandler(rec,
+		newConfirmRequest(t, authID, "wrong-csrf", "expected-csrf"),
+	)
+
+	assert.Equal(t, http.StatusForbidden, rec.Code,
+		"CSRF cookie/form mismatch must be rejected with 403")
+
+	// And the registration must still be pending — the rejected POST
+	// must not have called handleRegistration.
+	cached, ok := app.state.GetAuthCacheEntry(authID)
+	require.True(t, ok, "rejected POST must not evict the cached registration")
+	require.NotNil(t, cached.PendingConfirmation(),
+		"rejected POST must not clear the pending confirmation")
+}
+
+// TestRegisterConfirmHandler_RejectsWithoutPending verifies that
+// /register/confirm refuses to finalise a registration that did not
+// first complete the OIDC interstitial. Without this check an attacker
+// who knew an auth_id could POST directly to the confirm endpoint and
+// claim the device.
+func TestRegisterConfirmHandler_RejectsWithoutPending(t *testing.T) {
+	t.Parallel()
+
+	app := createTestApp(t)
+	provider := &AuthProviderOIDC{h: app}
+
+	authID := types.MustAuthID()
+	// Cached registration with NO pending confirmation set — i.e. the
+	// OIDC callback has not run yet.
+	app.state.SetAuthCacheEntry(authID, types.NewRegisterAuthRequest(
+		&types.RegistrationData{Hostname: "no-oidc-yet"},
+	))
+
+	rec := httptest.NewRecorder()
+	provider.RegisterConfirmHandler(rec,
+		newConfirmRequest(t, authID, "fake", "fake"),
+	)
+
+	assert.Equal(t, http.StatusForbidden, rec.Code,
+		"confirm without prior OIDC pending state must be rejected with 403")
+}

hscontrol/templates/register_confirm.go

@@ -0,0 +1,101 @@
+package templates
+
+import (
+	"github.com/chasefleming/elem-go"
+	"github.com/chasefleming/elem-go/attrs"
+)
+
+// RegisterConfirmInfo carries the human-readable information shown on
+// the registration confirmation interstitial that an OIDC-authenticated
+// user must explicitly accept before a pending node is registered to
+// their identity. The fields here intentionally include enough device
+// detail (hostname, OS, machine-key fingerprint) for the user to
+// recognise whether the device they are about to claim is in fact
+// theirs.
+type RegisterConfirmInfo struct {
+	// FormAction is the absolute or relative URL the confirm form
+	// POSTs to. Typically /register/confirm/{auth_id}.
+	FormAction string
+
+	// CSRFTokenName is the name of the hidden form field carrying the
+	// CSRF token. The corresponding cookie shares this name.
+	CSRFTokenName string
+
+	// CSRFToken is the per-session token that must match the value of
+	// the cookie set by the OIDC callback before the POST is honoured.
+	CSRFToken string
+
+	// User is the OIDC-authenticated identity the device will be
+	// registered to if the user confirms.
+	User string
+
+	// Hostname is the hostname the registering tailscaled instance
+	// reported in its RegisterRequest.
+	Hostname string
+
+	// OS is the operating system the registering tailscaled reported.
+	// May be the empty string when the client did not send Hostinfo.
+	OS string
+
+	// MachineKey is the short fingerprint of the registering machine
+	// key. The full key is intentionally not shown.
+	MachineKey string
+}
+
+// RegisterConfirm renders an interstitial page that asks the
+// OIDC-authenticated user to explicitly confirm that they want to
+// register the named device under their account. Without this
+// confirmation step a single GET to /register/{auth_id} could
+// silently complete a phishing-style registration when the victim's
+// IdP allows silent SSO.
+func RegisterConfirm(info RegisterConfirmInfo) *elem.Element {
+	deviceList := elem.Ul(nil,
+		elem.Li(nil, elem.Strong(nil, elem.Text("Hostname: ")), elem.Text(info.Hostname)),
+		elem.Li(nil, elem.Strong(nil, elem.Text("OS: ")), elem.Text(displayOrUnknown(info.OS))),
+		elem.Li(nil, elem.Strong(nil, elem.Text("Machine key: ")), Code(elem.Text(info.MachineKey))),
+		elem.Li(nil, elem.Strong(nil, elem.Text("Will be registered to: ")), elem.Text(info.User)),
+	)
+
+	form := elem.Form(
+		attrs.Props{
+			attrs.Method: "POST",
+			attrs.Action: info.FormAction,
+		},
+		elem.Input(attrs.Props{
+			attrs.Type:  "hidden",
+			attrs.Name:  info.CSRFTokenName,
+			attrs.Value: info.CSRFToken,
+		}),
+		elem.Button(
+			attrs.Props{attrs.Type: "submit"},
+			elem.Text("Confirm registration"),
+		),
+	)
+
+	return HtmlStructure(
+		elem.Title(nil, elem.Text("Headscale - Confirm node registration")),
+		mdTypesetBody(
+			headscaleLogo(),
+			H2(elem.Text("Confirm node registration")),
+			P(elem.Text(
+				"A device is asking to be added to your tailnet. "+
+					"Please review the details below and confirm that this device is yours.",
+			)),
+			deviceList,
+			form,
+			P(elem.Text(
+				"If you do not recognise this device, close this window. "+
+					"The registration request will expire automatically.",
+			)),
+			pageFooter(),
+		),
+	)
+}
+
+func displayOrUnknown(s string) string {
+	if s == "" {
+		return "(unknown)"
+	}
+
+	return s
+}

hscontrol/types/common.go

@@ -230,6 +230,22 @@ type SSHCheckBinding struct {
 	DstNodeID NodeID
 }
 
+// PendingRegistrationConfirmation captures the server-side state needed
+// to finalise a node registration after the user has confirmed it on
+// the OIDC interstitial. The OIDC callback resolves the user identity
+// and node expiry, stores them on the cached AuthRequest, and renders
+// a confirmation page; only when the user POSTs the confirmation form
+// does the actual node registration run.
+//
+// CSRF is a one-shot per-session token that the OIDC callback set
+// both as a cookie and as a hidden form field. The confirm POST
+// handler refuses to proceed unless the cookie and form values match.
+type PendingRegistrationConfirmation struct {
+	UserID     uint
+	NodeExpiry *time.Time
+	CSRF       string
+}
+
 // AuthRequest represents a pending authentication request from a user or a
 // node. It carries the minimum data needed to either complete a node
 // registration (regData populated) or an SSH check-mode auth (sshBinding
@@ -257,6 +273,13 @@ type AuthRequest struct {
 	// safely.
 	sshBinding *SSHCheckBinding
 
+	// pendingConfirmation is populated by the OIDC callback for the
+	// node-registration flow once the user identity has been resolved
+	// but before the user has explicitly confirmed the registration on
+	// the interstitial. The /register/confirm POST handler reads it to
+	// finalise the registration without re-running the OIDC flow.
+	pendingConfirmation *PendingRegistrationConfirmation
+
 	finished chan AuthVerdict
 	closed   *atomic.Bool
 }
@@ -331,6 +354,22 @@ func (rn *AuthRequest) IsSSHCheck() bool {
 	return rn.sshBinding != nil
 }
 
+// SetPendingConfirmation marks this AuthRequest as having an
+// OIDC-resolved user that is waiting to confirm the registration on
+// the interstitial. The OIDC callback should call this and then render
+// the confirmation page; the /register/confirm POST handler reads the
+// stored UserID/NodeExpiry to finish the registration.
+func (rn *AuthRequest) SetPendingConfirmation(p *PendingRegistrationConfirmation) {
+	rn.pendingConfirmation = p
+}
+
+// PendingConfirmation returns the pending OIDC-resolved registration
+// state captured by SetPendingConfirmation, or nil if no OIDC callback
+// has yet resolved an identity for this AuthRequest.
+func (rn *AuthRequest) PendingConfirmation() *PendingRegistrationConfirmation {
+	return rn.pendingConfirmation
+}
+
 func (rn *AuthRequest) FinishAuth(verdict AuthVerdict) {
 	if rn.closed.Swap(true) {
 		return

hscontrol/types/common_test.go

@@ -57,6 +57,27 @@ func TestNewAuthRequestEmptyPayload(t *testing.T) {
 	assert.Panics(t, func() { _ = req.SSHCheckBinding() })
 }
 
+// TestPendingRegistrationConfirmation verifies that the OIDC callback
+// can stash a pending confirmation onto an AuthRequest and that the
+// /register/confirm POST handler can read it back unchanged.
+func TestPendingRegistrationConfirmation(t *testing.T) {
+	req := NewRegisterAuthRequest(&RegistrationData{Hostname: "phish-test"})
+
+	require.Nil(t, req.PendingConfirmation(),
+		"new AuthRequest must have no pending confirmation")
+
+	pending := &PendingRegistrationConfirmation{
+		UserID: 42,
+		CSRF:   "csrf-marker",
+	}
+	req.SetPendingConfirmation(pending)
+
+	got := req.PendingConfirmation()
+	require.NotNil(t, got, "PendingConfirmation must return the stored value")
+	assert.Equal(t, uint(42), got.UserID)
+	assert.Equal(t, "csrf-marker", got.CSRF)
+}
+
 func TestDefaultBatcherWorkersFor(t *testing.T) {
 	tests := []struct {
 		cpuCount int

integration/scenario.go

@@ -1189,9 +1189,118 @@ func doLoginURLWithClient(hostname string, loginURL *url.URL, hc *http.Client, f
 		}
 	}
 
+	// The OIDC registration flow now renders a confirmation interstitial
+	// (POST form) instead of completing immediately. Detect the form and
+	// auto-submit it so integration tests behave like a real browser.
+	if followRedirects && strings.Contains(body, `action="/register/confirm/`) {
+		confirmBody, confirmURL, confirmErr := submitConfirmForm(hostname, body, resp, hc)
+		if confirmErr != nil {
+			return body, redirectURL, confirmErr
+		}
+
+		return confirmBody, confirmURL, nil
+	}
+
 	return body, redirectURL, nil
 }
 
+// submitConfirmForm parses the OIDC registration confirmation
+// interstitial HTML, extracts the form action and CSRF token, and
+// POSTs the form using the same HTTP client (which carries the CSRF
+// cookie set by the callback).
+func submitConfirmForm(
+	hostname string,
+	htmlBody string,
+	prevResp *http.Response,
+	hc *http.Client,
+) (string, *url.URL, error) {
+	// Extract form action URL.
+	actionIdx := strings.Index(htmlBody, `action="`)
+	if actionIdx == -1 {
+		return "", nil, fmt.Errorf("%s confirm form: no action attribute", hostname) //nolint:err113
+	}
+
+	actionStart := actionIdx + len(`action="`)
+
+	actionEnd := strings.Index(htmlBody[actionStart:], `"`)
+	if actionEnd == -1 {
+		return "", nil, fmt.Errorf("%s confirm form: unterminated action attribute", hostname) //nolint:err113
+	}
+
+	formAction := htmlBody[actionStart : actionStart+actionEnd]
+
+	// Extract hidden CSRF input value. The rendered <input> has
+	// attributes in name-type-value order so we grab the whole tag.
+	before, _, ok := strings.Cut(htmlBody, `name="headscale_register_confirm"`)
+	if !ok {
+		return "", nil, fmt.Errorf("%s confirm form: no CSRF input", hostname) //nolint:err113
+	}
+
+	tagStart := strings.LastIndex(before, "<input")
+	if tagStart == -1 {
+		return "", nil, fmt.Errorf("%s confirm form: no input tag for CSRF", hostname) //nolint:err113
+	}
+
+	tagEnd := strings.Index(htmlBody[tagStart:], ">")
+	if tagEnd == -1 {
+		return "", nil, fmt.Errorf("%s confirm form: unterminated input tag", hostname) //nolint:err113
+	}
+
+	inputTag := htmlBody[tagStart : tagStart+tagEnd+1]
+
+	valIdx := strings.Index(inputTag, `value="`)
+	if valIdx == -1 {
+		return "", nil, fmt.Errorf("%s confirm form: no value in CSRF input", hostname) //nolint:err113
+	}
+
+	valStart := valIdx + len(`value="`)
+	valEnd := strings.Index(inputTag[valStart:], `"`)
+	csrfToken := inputTag[valStart : valStart+valEnd]
+
+	// Build the absolute POST URL from the response's request URL.
+	base := prevResp.Request.URL
+	confirmURL := &url.URL{
+		Scheme: base.Scheme,
+		Host:   base.Host,
+		Path:   formAction,
+	}
+
+	log.Printf("%s auto-submitting confirm form: %s", hostname, confirmURL)
+
+	formData := url.Values{
+		"headscale_register_confirm": {csrfToken},
+	}
+
+	ctx := context.Background()
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, confirmURL.String(), strings.NewReader(formData.Encode()))
+	if err != nil {
+		return "", nil, fmt.Errorf("%s creating confirm request: %w", hostname, err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	confirmResp, err := hc.Do(req)
+	if err != nil {
+		return "", nil, fmt.Errorf("%s sending confirm request: %w", hostname, err)
+	}
+	defer confirmResp.Body.Close()
+
+	confirmBytes, err := io.ReadAll(confirmResp.Body)
+	if err != nil {
+		return "", nil, fmt.Errorf("%s reading confirm response: %w", hostname, err)
+	}
+
+	if confirmResp.StatusCode != http.StatusOK {
+		return string(confirmBytes), nil, fmt.Errorf( //nolint:err113
+			"%s confirm returned status %d: %s",
+			hostname, confirmResp.StatusCode, string(confirmBytes),
+		)
+	}
+
+	return string(confirmBytes), nil, nil
+}
+
 var errParseAuthPage = errors.New("parsing auth page")
 
 func (s *Scenario) runHeadscaleRegister(userStr string, body string) error {