web: Referrer-Policy same-origin; a password shown once emptied on pagehide

D-B3. Fetch Standard § 3.2 "append a request `Origin` header": under
Referrer-Policy no-referrer a request that is not GET/HEAD and not CORS -
a form POST, a navigation - gets Origin "null". originAllowed() refuses
"null" whenever Sec-Fetch-Site is absent, and Fetch Metadata § 3 sends
Sec-Fetch-Site only to a potentially trustworthy URL: every form,
sign-in included, failed in Safari before 16.4 and in any browser on a
plain-HTTP panel at a name. same-origin nulls Origin only for a request
not same origin with its URL and still sends no referrer to another
site. The comments of the origin check say so.

D-B13. noStore keeps the page out of HTTP caches (RFC 9111 § 5.2.2.5);
a history mechanism "might honor" it (§ 6), and Pragma in a response
"was never specified" (§ 5.4) - it goes. CopyField.Secret marks the
password of out-app-created data-secret, and panel.js empties such
fields on pagehide (HTML § 7.5.9, "unload a Document", step 10.2: fired
whether or not the document is kept for history traversal).

Measured 2026-10-15 in Chrome 152 (the desktop app's browser), a local
probe page with Cache-Control: no-store and a data-secret field: Back
reloads it (pageshow persisted=false, a new load), so this browser keeps
no-store pages out of its back/forward cache; the handler, fired on the
same page, empties the field. Firefox and Safari not measured.

Tests: the header value; the created page has the password data-secret
and the login not, no Pragma. Stand (2026-10-15, make e2e, exit 0): new
form_post_with_the_browsers_origin - Referrer-Policy: same-origin on a
page; a POST carrying the page's own Origin and no Sec-Fetch-Site, what
a browser sends now, passes; one carrying Origin: null, what it sent
before, is 403. (A first run failed where the e2e client and a view test
scraped the old input markup; both read data-secret now.) go vet and go
test ./... pass on the server (24 packages).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -131,6 +131,16 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   copy, names a renewal waiting in the mount, and warns when it has waited
   longer than the daily check allows; the expiry notice is not sent while a
   renewal waits on time (assumptions A-65).
+- **The panel works in browsers that do not say where a request comes
+  from.** The panel's `Referrer-Policy: no-referrer` made a browser send a
+  form's `Origin` as `null`, which the panel refuses unless the browser also
+  sends `Sec-Fetch-Site`: in Safari before 16.4, or in any browser on a
+  panel served over plain HTTP at a name, every form - signing in
+  included - was refused. The policy is now `same-origin`, which still
+  sends nothing to other sites (assumptions D-B3).
+- **A password shown once is emptied when its page is left,** so a browser
+  that keeps the page for its Back button shows an empty field; the
+  meaningless `Pragma` header goes (assumptions D-B13).
 - **Words for what happens to mail match Postfix's.** A message refused with
   a temporary error while the panel or the spam filter does not answer was
   called deferred, which in Postfix's words is mail waiting in its queue;

docs/architecture.md

@@ -776,7 +776,7 @@ are in [plans/panel-redesign.md](plans/panel-redesign.md) § Enforcement.
 on every response: `Content-Security-Policy: default-src 'self'; object-src
 'none'; base-uri 'none'; form-action 'self'; frame-ancestors 'none'`,
 `X-Content-Type-Options: nosniff`, `X-Frame-Options: DENY`,
-`Referrer-Policy: no-referrer`, and `Strict-Transport-Security` when the cookie
+`Referrer-Policy: same-origin`, and `Strict-Transport-Security` when the cookie
 is `Secure`. Because the policy has no exemptions, no template carries an
 inline `<script>`, an event-handler attribute or `style="…"` — the page's
 behaviour is `htmx.min.js` plus `panel.js` (copy and *fill* buttons, the

docs/audit-2026-10-12.md

@@ -989,12 +989,16 @@ those after it move up one patch number each.
    connection is silent in all three milters (libmilter read: sendmail
    8.17.1.9 fetched into dev/upstream); the expiry notice waits for a renewal
    that is on time.
-- [ ] **The panel in browsers without Sec-Fetch-Site** (D-B3, D-B13): under
+- [x] **The panel in browsers without Sec-Fetch-Site** (D-B3, D-B13): under
    `Referrer-Policy: no-referrer` a form POST carries `Origin: null`, which
    the origin check refuses - every POST, sign-in included, fails in Safari
    before 16.4 and over plain HTTP at a name; `same-origin` instead, with a
    header test and one POST on the stand. A shown-once secret is blanked on
    `pagehide`; `Pragma` goes. - **Opus**
+   *Done 2026-10-15.* Measured the same day in Chrome 152 (the desktop
+   app's browser): a `no-store` page is not restored from the back/forward
+   cache (pageshow persisted=false, a fresh load); the `pagehide` handler is
+   for browsers that do restore one. Firefox and Safari not measured.
 - [ ] **Two processes opening an old database** (D-S3): `user_version` is
    read outside the transaction, so the panel and dmarc-ingest can both
    run one migration; `_txlock=immediate` and the version re-read inside

docs/roadmap.md

@@ -42,7 +42,7 @@ in `git log` and [CHANGELOG.md](../CHANGELOG.md).
 | from-header-binding | Hold a message's `From:` header against the application that sends it | shipped `2.4.0` | 9/9 | [plans/from-header-binding.md](plans/from-header-binding.md) |
 | panel-redesign | Panel redesign (accepted mockups, design contract) | shipped `2.0.0` | 27/27 | [plans/panel-redesign.md](plans/panel-redesign.md) |
 | schema-squash | Squash SQLite migrations into a 2.x baseline | built in panel-redesign (stage 1) | — | [plans/panel-redesign.md](plans/panel-redesign.md) |
-| audit-2026-10-12 | Follow-ups of the 2026-10-12 full-tree code audit, seven stages | in progress (stage 0 shipped `2.4.2`, stages 1+2 `2.5.0`, 2b `2.5.1`; next stage 2c → `2.5.2`) | 41/81 | [audit-2026-10-12.md](audit-2026-10-12.md) |
+| audit-2026-10-12 | Follow-ups of the 2026-10-12 full-tree code audit, seven stages | in progress (stage 0 shipped `2.4.2`, stages 1+2 `2.5.0`, 2b `2.5.1`; next stage 2c → `2.5.2`) | 42/81 | [audit-2026-10-12.md](audit-2026-10-12.md) |
 
 **Recommended order** (not binding; owner, 2026-10-09: feature order follows
 development convenience): **panel-redesign** shipped as `2.0.0` (2026-10-11) and

internal/web/handlers/handlers_apps.go

@@ -393,14 +393,15 @@ func (h *Handlers) recalcApp(appID int64) error {
 	return h.recalcRateLimit(store.RateLimitScopeApp, appID)
 }
 
-// noStore keeps a page that shows a secret out of every cache and out of the
-// browser's history copy: the password on it is shown once.
-// RFC 9111 § 5.2.2.5: no-store keeps it out of every HTTP cache, private and
-// shared. The history part is not what it governs (§ 6), and Pragma has no
-// defined meaning in a response (§ 5.4): assumptions-2026-10-14, D-B13.
+// noStore keeps a page that shows a secret out of every HTTP cache, private
+// and shared (RFC 9111 § 5.2.2.5): the password on it is shown once. A
+// browser's history - the back/forward cache - is not what it governs: § 6,
+// a history mechanism "might honor" no-store. So the page's field is also
+// marked secret, and panel.js empties it when the page is left (pagehide).
+// No Pragma: in a response it "was never specified" (§ 5.4). Assumptions
+// D-B13.
 func noStore(w http.ResponseWriter) {
 	w.Header().Set("Cache-Control", "no-store")
-	w.Header().Set("Pragma", "no-cache")
 }
 
 // blankAppForm is the application form as it opens: any address of the domain,

internal/web/handlers/handlers_outbound_pages_test.go

@@ -314,11 +314,11 @@ func TestPasswordIsShownOnceAndNeverCached(t *testing.T) {
 	rec := postFormAs(s.h.HandleApplicationCreate, globalPrincipal, "/outbound/domains/1/applications/new", s.paths, url.Values{
 		"login": {"prod-server"}, "mode": {"list"}, "addresses": {"alerts@example.org"},
 	})
-	if rec.Code != http.StatusCreated || rec.Header().Get("Cache-Control") != "no-store" || rec.Header().Get("Pragma") != "no-cache" {
+	if rec.Code != http.StatusCreated || rec.Header().Get("Cache-Control") != "no-store" || rec.Header().Get("Pragma") != "" {
 		t.Fatalf("create = %d, Cache-Control %q", rec.Code, rec.Header().Get("Cache-Control"))
 	}
 	password := s.sasl["prod-server"]
-	has(t, "created", rec.Body.String(), `<h2>Shown once</h2>`, `value="`+password+`"`, `value="prod-server"`,
+	has(t, "created", rec.Body.String(), `<h2>Shown once</h2>`, `value="`+password+`" data-secret>`, `value="prod-server">`,
 		`If this one is lost, generate another from the application&#39;s page.`, `alerts@example.org`, `465 SSL/TLS · 587 STARTTLS`,
 		`href="/outbound/domains/1">Done — back to example.org</a>`)
 	lacks(t, "created", rec.Body.String(), `stopped working`)

internal/web/security.go

@@ -65,10 +65,17 @@ func (s *Server) secure(next http.Handler) http.Handler {
 		// CSP3 § 6.4.2.2: 'none' is DENY, and where frame-ancestors is
 		// enforced X-Frame-Options is ignored.
 		h.Set("X-Frame-Options", "DENY")
-		// The panel's behaviour never depends on the referrer, so the strictest
-		// value is free: panel URLs carry domain names and record identifiers
-		// that need not leak to anything the administrator clicks through to.
-		h.Set("Referrer-Policy", "no-referrer")
+		// Panel URLs carry domain names and record identifiers that need not
+		// leak to anything the administrator clicks through to: same-origin
+		// sends no referrer to another site. Not no-referrer, which the
+		// origin check below depends on: under it a browser sends a form
+		// POST - a navigation - with Origin: null, refused whenever
+		// Sec-Fetch-Site is absent (Safari before 16.4, any browser over
+		// plain HTTP at a name). Fetch Standard § 3.2 "append a request
+		// `Origin` header": "no-referrer" sets the serialised origin to null;
+		// "same-origin" does so only when the request is not same origin
+		// with its URL (assumptions D-B3).
+		h.Set("Referrer-Policy", "same-origin")
 		if s.cfg.CookieSecure {
 			h.Set("Strict-Transport-Security", strictTransportSecurity)
 		}
@@ -131,8 +138,9 @@ func originAllowed(r *http.Request) bool {
 	// Older browsers send only Origin, and so does a current one over plain
 	// HTTP at a name other than localhost: Fetch Metadata § 3 appends its
 	// headers only for a potentially trustworthy URL. Fetch Standard § 3.2: a
-	// request that is neither GET nor HEAD carries Origin. (Which value it
-	// carries under this panel's Referrer-Policy: assumptions-2026-10-14, D-B3.)
+	// request that is neither GET nor HEAD carries Origin, and under this
+	// panel's Referrer-Policy, same-origin, it is the page's own origin for a
+	// form of the panel (§ 3.2; assumptions-2026-10-14, D-B3).
 	// Compare hosts, not full origins: the panel speaks plain HTTP behind the
 	// proxy and does not know its own external scheme, while Origin will say
 	// https.
@@ -154,7 +162,8 @@ func originAllowed(r *http.Request) bool {
 		// Fetch Standard § 2.2.5 "serializing a request origin": "null" for a
 		// redirect-tainted request; HTML § 7.1.1: an opaque origin serialises
 		// to "null"; url.Parse("null") has no Host. (Fetch § 3.2 also sends
-		// "null" under Referrer-Policy no-referrer: D-B3 of the same register.)
+		// "null" under Referrer-Policy no-referrer, which this panel therefore
+		// does not set: D-B3 of the same register.)
 		return false
 	}
 	return u.Host == r.Host

internal/web/security_test.go

@@ -93,7 +93,7 @@ func TestSecurityHeaders(t *testing.T) {
 		"Content-Security-Policy":   contentSecurityPolicy,
 		"X-Content-Type-Options":    "nosniff",
 		"X-Frame-Options":           "DENY",
-		"Referrer-Policy":           "no-referrer",
+		"Referrer-Policy":           "same-origin",
 		"Strict-Transport-Security": strictTransportSecurity,
 	}
 	for name, value := range want {

internal/web/view/components.go

@@ -405,6 +405,10 @@ type CopyField struct {
 	Value string
 	Rows  int
 	Help  Text
+	// Secret marks a value shown once: panel.js empties the field when the
+	// page is left, so a page the browser restores from its back/forward
+	// cache does not show it again.
+	Secret bool
 }
 
 // Fact is the input of facts (as a slice): a label and its value. Mono sets the

internal/web/view/outbound_app.go

@@ -270,7 +270,7 @@ func NewOutAppCreated(m Meta, domainID int64, domain, login, password string, fr
 			Title: "New password for", Code: login},
 		Credential: Box{Icon: "ti-eye", Title: "Shown once", End: Plain("Not stored — copy it now"), Variant: BoxCredential},
 		Login:      CopyField{Label: "Login", Value: login},
-		Password:   CopyField{Label: "Password", Value: password, Help: help},
+		Password:   CopyField{Label: "Password", Value: password, Help: help, Secret: true},
 		Done:       Foot{Button: &Action{Label: "Done — back to " + domain, Href: DomainHref(domainID), Primary: true}},
 		Connect:    Box{Icon: "ti-plug", Title: "Connect with"},
 		Facts: []Fact{

internal/web/view/outbound_test.go

@@ -400,7 +400,7 @@ func TestOutAppCreatedShowsLoginAndPasswordOnce(t *testing.T) {
 	pageHas(t, "New password", out,
 		`<h1 class="title is-3">New password for <span class="sp-mono">prod-server</span></h1>`,
 		`<div class="box sp-credential">`, `<h2>Shown once</h2>`, `Not stored — copy it now`, `ti-eye`,
-		`<input class="input" readonly value="prod-server">`, `<input class="input" readonly value="kT7v-Qm2x-Lp9d-Ue4s-Hn6b-Rz3w">`,
+		`<input class="input" readonly value="prod-server">`, `<input class="input" readonly value="kT7v-Qm2x-Lp9d-Ue4s-Hn6b-Rz3w" data-secret>`,
 		`The previous password stopped working when this one was generated.`,
 		`href="/outbound/domains/1">Done — back to example.org</a>`,
 		`<h2>Connect with</h2>`, `mail.example.org`, `465 SSL/TLS · 587 STARTTLS`, `*@example.org`,

internal/web/view/static/panel.js

@@ -63,6 +63,22 @@
     input.focus();
   });
 
+  // --- Secrets shown once ------------------------------------------------
+  // A password shown once is in a field marked data-secret. Cache-Control:
+  // no-store keeps the page out of HTTP caches, but a browser may still keep
+  // the page in its back/forward cache and show it again on Back (RFC 9111
+  // § 6: a history mechanism "might honor" no-store). Emptying the field when
+  // the page is left means a restored page shows nothing to copy. HTML Living
+  // Standard, § 7.5.9 "Unloading documents", "unload a Document", step 10.2:
+  // pagehide is fired whether or not the document is kept for later history
+  // traversal (its salvageable state, the event's persisted).
+  window.addEventListener("pagehide", function () {
+    var secrets = document.querySelectorAll("[data-secret]");
+    for (var i = 0; i < secrets.length; i++) {
+      secrets[i].value = "";
+    }
+  });
+
   // --- Confirmation on destructive forms --------------------------------
   // Forms that delete something or invalidate a working credential carry a
   // data-confirm message. The prompt lives here rather than in an inline

internal/web/view/templates/components.html

@@ -155,7 +155,7 @@
      CopyField): one line, or a textarea when Rows is set — a DKIM key. The
      button is wired by panel.js through data-copy. */}}
 {{define "copy_field"}}<div class="field"><label class="label">{{.Label}}</label>
-<div class="field has-addons"><div class="control is-expanded">{{if .Rows}}<textarea class="textarea" rows="{{.Rows}}" readonly>{{.Value}}</textarea>{{else}}<input class="input" readonly value="{{.Value}}">{{end}}</div><div class="control"><button type="button" class="button" data-copy><i class="ti ti-copy"></i>Copy</button></div></div>
+<div class="field has-addons"><div class="control is-expanded">{{if .Rows}}<textarea class="textarea" rows="{{.Rows}}" readonly{{if .Secret}} data-secret{{end}}>{{.Value}}</textarea>{{else}}<input class="input" readonly value="{{.Value}}"{{if .Secret}} data-secret{{end}}>{{end}}</div><div class="control"><button type="button" class="button" data-copy><i class="ti ti-copy"></i>Copy</button></div></div>
 {{if .Help}}<p class="help">{{template "inline" .Help}}</p>
 {{end}}</div>{{end}}
 

test/e2e/health_served_test.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"math/big"
 	"net"
+	"net/http"
 	"os"
 	"path/filepath"
 	"strings"
@@ -137,3 +138,41 @@ func writeCertWithoutItsKey(certPath string, notAfter time.Time) error {
 	}
 	return os.WriteFile(certPath, pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}), 0o644)
 }
+
+// testFormPostWithTheBrowsersOrigin: a browser on a plain-HTTP panel at a
+// name sends no Sec-Fetch-Site (Fetch Metadata § 3: only for a potentially
+// trustworthy URL), and its form POST - a navigation - carries Origin by the
+// page's Referrer-Policy (Fetch Standard § 3.2): its own origin under the
+// panel's same-origin, which passes; "null" under no-referrer, which the
+// panel sent until 2.5.2 and which the origin check refuses (assumptions
+// D-B3). The client here is not a browser: it sends what one would.
+func testFormPostWithTheBrowsersOrigin(t *testing.T, sc *scenario) {
+	resp, _, err := sc.panel.get("/server/health")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := resp.Header.Get("Referrer-Policy"); got != "same-origin" {
+		t.Fatalf("Referrer-Policy %q, want same-origin", got)
+	}
+	post := func(origin string) int {
+		t.Helper()
+		req, err := http.NewRequest(http.MethodPost, panelBaseURL+"/server/health/recheck", strings.NewReader(""))
+		if err != nil {
+			t.Fatal(err)
+		}
+		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+		req.Header.Set("Origin", origin)
+		resp, err := sc.panel.http.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp.Body.Close()
+		return resp.StatusCode
+	}
+	if code := post(panelBaseURL); code != http.StatusOK {
+		t.Fatalf("POST with the page's own Origin: status %d, want 200 after the redirect", code)
+	}
+	if code := post("null"); code != http.StatusForbidden {
+		t.Fatalf("POST with Origin: null: status %d, want 403", code)
+	}
+}

test/e2e/main_test.go

@@ -174,6 +174,9 @@ func TestE2E(t *testing.T) {
 	run("health_shows_what_is_served", func(t *testing.T) {
 		testHealthShowsWhatIsServed(t, sc)
 	})
+	run("form_post_with_the_browsers_origin", func(t *testing.T) {
+		testFormPostWithTheBrowsersOrigin(t, sc)
+	})
 
 	run("inbound_ui_absent_when_disabled", func(t *testing.T) {
 		resp, body, err := sc.panel.get("/overview")

test/e2e/panel_client.go

@@ -264,7 +264,7 @@ func (c *panelClient) applicationID(domainID, login string) (string, error) {
 // before returning.
 func extractCodeRow(body, label string) (string, bool) {
 	pattern := `<label class="label">` + regexp.QuoteMeta(label) + `</label>\s*<div class="field has-addons"><div class="control is-expanded">` +
-		`(?:<input class="input" readonly value="([^"]*)">|<textarea class="textarea" rows="\d+" readonly>([^<]*)</textarea>)`
+		`(?:<input class="input" readonly value="([^"]*)"(?: data-secret)?>|<textarea class="textarea" rows="\d+" readonly(?: data-secret)?>([^<]*)</textarea>)`
 	m := regexp.MustCompile(pattern).FindStringSubmatch(body)
 	if m == nil {
 		return "", false