diff --git a/.gitea/workflows/deploy.yaml b/.gitea/workflows/deploy.yaml
index 1f9dfae..5c53711 100644
--- a/.gitea/workflows/deploy.yaml
+++ b/.gitea/workflows/deploy.yaml
@@ -31,6 +31,9 @@ jobs:
       # origin, e.g. https://big-auth.labs.respellion.tech (runbook, "Publishing
       # through the labs Caddy").
       KEYCLOAK_URL: ${{ vars.KEYCLOAK_URL }}
+      # `true` fills in the medewerker OTP step for the public demo (chart value
+      # demo.otpAutofill). The fixture secret is committed: demo only.
+      OTP_AUTOFILL: ${{ vars.OTP_AUTOFILL }}
     steps:
       - uses: https://github.com/actions/checkout@v4
 
@@ -97,7 +100,7 @@ jobs:
           make k8s-reseed \
             TALOS_HOST=${TALOS_HOST:-localhost} \
             K8S_REGISTRY=${TALOS_VM_IP:-192.168.122.173}:30500 \
-            K8S_SET="${KEYCLOAK_URL:+--set keycloakUrl=$KEYCLOAK_URL}"
+            K8S_SET="${KEYCLOAK_URL:+--set keycloakUrl=$KEYCLOAK_URL} --set demo.otpAutofill=${OTP_AUTOFILL:-false}"
 
       # `dev` is a mutable tag and helm sees an unchanged pod template, so the
       # new images only land on a restart (pullPolicy is already Always).
diff --git a/docs/runbooks/kubernetes-talos.md b/docs/runbooks/kubernetes-talos.md
index 75b3c2b..d35a8f4 100644
--- a/docs/runbooks/kubernetes-talos.md
+++ b/docs/runbooks/kubernetes-talos.md
@@ -430,6 +430,18 @@ make k8s-up TALOS_HOST=localhost K8S_REGISTRY=<TALOS_HOST>:30500 \
 For deploy-on-merge, set the repository variable `KEYCLOAK_URL` to the same value.
 With it set, the `localhost` port-forwards (§5) no longer log in: the issuer is one string.
 
+Staff logins still hit the enforced OTP step. For a demo, set the repository variable
+`OTP_AUTOFILL=true` (chart value `demo.otpAutofill`): Keycloak then uses the `big-demo`
+theme, which fills in and submits the code from the fixture secret, so the step is visible
+but needs no authenticator. Keycloak restarts when the value flips. Demo only — the secret
+is committed.
+
+The theme lives in `infra/keycloak/themes/big-demo/` and is seeded as the `rr-kc-theme`
+ConfigMap by `infra/helm/seed-configmaps.sh` on every deploy. Keycloak runs `start-dev`,
+which doesn't cache themes, so an edit shows up about a minute after the ConfigMap changes.
+A *new* theme file also needs a key in the seed script and a path in the keycloak `files`
+in `values.yaml`.
+
 One-time setup:
 
 1. Fedora host: install `infra/development/big-portals-tunnel.service` from the Infra repo
diff --git a/infra/helm/big-reference/templates/_helpers.tpl b/infra/helm/big-reference/templates/_helpers.tpl
index 24bb55d..7efbf86 100644
--- a/infra/helm/big-reference/templates/_helpers.tpl
+++ b/infra/helm/big-reference/templates/_helpers.tpl
@@ -94,6 +94,10 @@ volumes:
       {{- with .defaultMode }}
       defaultMode: {{ . }}
       {{- end }}
+      {{- with .items }}
+      items:
+{{- toYaml . | nindent 8 }}
+      {{- end }}
 {{- end }}
 {{- with $w.data }}
   - name: data
@@ -125,13 +129,17 @@ volumes:
 {{/*
 Env list from a map. Every value is run through `tpl`, so values.yaml can name
 cluster-internal hosts ({{ .Release.Namespace }}) and the node address
-({{ .Values.host }}) without the chart hard-coding either.
+({{ .Values.host }}) without the chart hard-coding either. A value that renders
+empty is left out, which is how a setting is made conditional on a chart value.
 */}}
 {{- define "big.env" -}}
 {{- $root := index . 0 -}}
 {{- range $k, $v := index . 1 }}
+{{- $val := tpl (toString $v) $root }}
+{{- if $val }}
 - name: {{ $k }}
-  value: {{ tpl (toString $v) $root | quote }}
+  value: {{ $val | quote }}
+{{- end }}
 {{- end }}
 {{- end -}}
 
diff --git a/infra/helm/big-reference/values.yaml b/infra/helm/big-reference/values.yaml
index 31f4df4..1fb687f 100644
--- a/infra/helm/big-reference/values.yaml
+++ b/infra/helm/big-reference/values.yaml
@@ -30,6 +30,12 @@ host: 192.168.122.100
 # portals' authority (runbook, "Publishing through the labs Caddy").
 keycloakUrl: ""
 
+demo:
+  # Fill in and submit the medewerker OTP step from the fixture secret, so a public
+  # demo shows MFA enforced without an authenticator: makes the big-demo theme
+  # (infra/keycloak/themes/big-demo) Keycloak's default. Demo only: the secret is committed.
+  otpAutofill: false
+
 # Set when pulling from a private registry (e.g. the Gitea Container Registry).
 imagePullSecrets: []
 
@@ -277,11 +283,24 @@ workloads:
       # this issuer back, which is what browser tokens carry (infra/host-browser.yml).
       KC_HOSTNAME: '{{ include "big.keycloakUrl" . }}'
       KC_HOSTNAME_BACKCHANNEL_DYNAMIC: "true"
+      # Only rendered with demo.otpAutofill (big.env skips empty values); off, Keycloak
+      # keeps its stock theme and the mounted big-demo theme is unused.
+      KC_SPI_THEME_DEFAULT: '{{ if .Values.demo.otpAutofill }}big-demo{{ end }}'
     ports: [{ name: http, port: 8080 }]
     # TCP, not /health/ready on the management port: nothing here gates on realm
     # import, and a wrong health path would leave the Service with no endpoints.
     probe: { tcpSocket: { port: 8080 }, initialDelaySeconds: 15 }
-    files: [{ configMap: rr-kc-realms, mountPath: /opt/keycloak/data/import }]
+    files:
+      - { configMap: rr-kc-realms, mountPath: /opt/keycloak/data/import }
+      # infra/keycloak/themes/big-demo, seeded by infra/helm/seed-configmaps.sh.
+      - configMap: rr-kc-theme
+        mountPath: /opt/keycloak/themes/big-demo
+        items:
+          - { key: login.properties, path: login/theme.properties }
+          - { key: otp-autofill.js, path: login/resources/js/otp-autofill.js }
+          - { key: account.properties, path: account/theme.properties }
+          - { key: admin.properties, path: admin/theme.properties }
+          - { key: email.properties, path: email/theme.properties }
 
   # ── Flowable (S-03) ─────────────────────────────────────────────────────────
   flowable-db:
diff --git a/infra/helm/seed-configmaps.sh b/infra/helm/seed-configmaps.sh
index 9dd9961..9d8f05e 100755
--- a/infra/helm/seed-configmaps.sh
+++ b/infra/helm/seed-configmaps.sh
@@ -30,6 +30,15 @@ seed() {  # name  <kubectl --from-file args...>
 seed rr-oz-config            --from-file="$repo/infra/openzaak/setup_configuration/"
 seed rr-nrc-config           --from-file="$repo/infra/opennotificaties/setup_configuration/"
 seed rr-kc-realms            --from-file="$repo/infra/keycloak/realms/"
+# The big-demo login theme (demo.otpAutofill). ConfigMap keys are flat, so each
+# file gets a key here and its path back in the keycloak `files` in values.yaml.
+theme="$repo/infra/keycloak/themes/big-demo"
+seed rr-kc-theme \
+  --from-file=login.properties="$theme/login/theme.properties" \
+  --from-file=otp-autofill.js="$theme/login/resources/js/otp-autofill.js" \
+  --from-file=account.properties="$theme/account/theme.properties" \
+  --from-file=admin.properties="$theme/admin/theme.properties" \
+  --from-file=email.properties="$theme/email/theme.properties"
 seed rr-objecttypen-config   --from-file="$repo/infra/objecttypen/setup_configuration/"
 seed rr-objecten-config      --from-file="$repo/infra/objecten/setup_configuration/"
 # register.py + the RegisterRecord JSON schema (the __pycache__ dir is skipped:
diff --git a/infra/keycloak/themes/big-demo/account/theme.properties b/infra/keycloak/themes/big-demo/account/theme.properties
new file mode 100644
index 0000000..50cacd7
--- /dev/null
+++ b/infra/keycloak/themes/big-demo/account/theme.properties
@@ -0,0 +1,4 @@
+# The chart makes big-demo the default for every theme type, and Keycloak does not
+# fall back for a type a theme lacks (the account page then fails), so each type is
+# declared as a plain child of Keycloak 26's own default.
+parent=keycloak.v3
diff --git a/infra/keycloak/themes/big-demo/admin/theme.properties b/infra/keycloak/themes/big-demo/admin/theme.properties
new file mode 100644
index 0000000..3430eff
--- /dev/null
+++ b/infra/keycloak/themes/big-demo/admin/theme.properties
@@ -0,0 +1,4 @@
+# The chart makes big-demo the default for every theme type, and Keycloak does not
+# fall back for a type a theme lacks (the admin page then fails), so each type is
+# declared as a plain child of Keycloak 26's own default.
+parent=keycloak.v2
diff --git a/infra/keycloak/themes/big-demo/email/theme.properties b/infra/keycloak/themes/big-demo/email/theme.properties
new file mode 100644
index 0000000..4abe495
--- /dev/null
+++ b/infra/keycloak/themes/big-demo/email/theme.properties
@@ -0,0 +1,4 @@
+# The chart makes big-demo the default for every theme type, and Keycloak does not
+# fall back for a type a theme lacks (the email page then fails), so each type is
+# declared as a plain child of Keycloak 26's own default.
+parent=keycloak
diff --git a/infra/keycloak/themes/big-demo/login/resources/js/otp-autofill.js b/infra/keycloak/themes/big-demo/login/resources/js/otp-autofill.js
new file mode 100644
index 0000000..e46ed1b
--- /dev/null
+++ b/infra/keycloak/themes/big-demo/login/resources/js/otp-autofill.js
@@ -0,0 +1,24 @@
+// RFC 6238 with Keycloak's default policy (HmacSHA1, 6 digits, 30 s) over the
+// raw bytes of the medewerker fixture secret — same as tests/e2e/keycloak-login.ts.
+document.addEventListener('DOMContentLoaded', async () => {
+  const input = document.querySelector('input[name="otp"]');
+  if (!input || !input.form) return;
+  const key = await crypto.subtle.importKey('raw',
+    new TextEncoder().encode('BIGMEDEWERKEROTPSEED'), { name: 'HMAC', hash: 'SHA-1' }, false, ['sign']);
+  // A code is single-use, so a second login in the same window spends the next
+  // counter (Keycloak's look-ahead accepts it). Past that, fill but don't submit,
+  // so a rejected code can't turn into a submit loop.
+  const now = Math.floor(Date.now() / 30000);
+  let last = -1;
+  try { last = Number(sessionStorage.getItem('big-otp-counter')) || -1; } catch {}
+  const counter = Math.max(now, last + 1);
+  const msg = new DataView(new ArrayBuffer(8));
+  msg.setBigUint64(0, BigInt(counter));
+  const mac = new Uint8Array(await crypto.subtle.sign('HMAC', key, msg.buffer));
+  const o = mac[19] & 0x0f;
+  const n = ((mac[o] & 0x7f) << 24 | mac[o + 1] << 16 | mac[o + 2] << 8 | mac[o + 3]) % 1e6;
+  input.value = String(n).padStart(6, '0');
+  if (counter > now + 1) return;
+  try { sessionStorage.setItem('big-otp-counter', String(counter)); } catch {}
+  input.form.requestSubmit();
+});
diff --git a/infra/keycloak/themes/big-demo/login/theme.properties b/infra/keycloak/themes/big-demo/login/theme.properties
new file mode 100644
index 0000000..bfd5838
--- /dev/null
+++ b/infra/keycloak/themes/big-demo/login/theme.properties
@@ -0,0 +1,11 @@
+# Demo login theme for the public Talos deployment: keycloak.v2 plus a script that
+# fills in and submits the medewerker OTP step from the committed fixture secret
+# (docs/runbooks/keycloak.md). Only used when the chart's demo.otpAutofill is on —
+# it then becomes Keycloak's default theme. Never enable it anywhere real.
+#
+# Add styles, messages or template overrides here as in any Keycloak theme
+# (https://www.keycloak.org/ui-customization/themes); new files must also be
+# listed in infra/helm/seed-configmaps.sh and the keycloak `files` in values.yaml.
+parent=keycloak.v2
+import=common/keycloak
+scripts=js/otp-autofill.js