diff --git a/services/communication/guest-register-shared-secret-ensure-job.yaml b/services/communication/guest-register-shared-secret-ensure-job.yaml
new file mode 100644
index 0000000..06f2440
--- /dev/null
+++ b/services/communication/guest-register-shared-secret-ensure-job.yaml
@@ -0,0 +1,86 @@
+# services/communication/guest-register-shared-secret-ensure-job.yaml
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: guest-register-secret-writer
+  namespace: comms
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: guest-register-secret-writer
+  namespace: comms
+rules:
+  - apiGroups: [""]
+    resources: ["secrets"]
+    resourceNames: ["guest-register-shared-secret-runtime"]
+    verbs: ["get", "patch", "update"]
+  - apiGroups: [""]
+    resources: ["secrets"]
+    verbs: ["create"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: guest-register-secret-writer
+  namespace: comms
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: Role
+  name: guest-register-secret-writer
+subjects:
+  - kind: ServiceAccount
+    name: guest-register-secret-writer
+    namespace: comms
+---
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: guest-register-shared-secret-ensure-1
+  namespace: comms
+spec:
+  backoffLimit: 2
+  template:
+    spec:
+      serviceAccountName: guest-register-secret-writer
+      restartPolicy: OnFailure
+      volumes:
+        - name: work
+          emptyDir: {}
+      initContainers:
+        - name: generate
+          image: alpine:3.20
+          command: ["/bin/sh", "-c"]
+          args:
+            - |
+              set -euo pipefail
+              umask 077
+              dd if=/dev/urandom bs=32 count=1 2>/dev/null | od -An -tx1 | tr -d ' \n' > /work/secret
+              chmod 0644 /work/secret
+          volumeMounts:
+            - name: work
+              mountPath: /work
+      containers:
+        - name: write
+          image: bitnami/kubectl:latest
+          command: ["/bin/sh", "-c"]
+          args:
+            - |
+              set -euo pipefail
+              if kubectl -n comms get secret guest-register-shared-secret-runtime >/dev/null 2>&1; then
+                if kubectl -n comms get secret guest-register-shared-secret-runtime -o jsonpath='{.data.secret}' 2>/dev/null | grep -q .; then
+                  exit 0
+                fi
+              else
+                kubectl -n comms create secret generic guest-register-shared-secret-runtime \
+                  --from-file=secret=/work/secret >/dev/null
+                exit 0
+              fi
+
+              secret_b64="$(base64 /work/secret | tr -d '\n')"
+              payload="$(printf '{\"data\":{\"secret\":\"%s\"}}' \"${secret_b64}\")"
+              kubectl -n comms patch secret guest-register-shared-secret-runtime --type=merge -p \"${payload}\" >/dev/null
+          volumeMounts:
+            - name: work
+              mountPath: /work
+
diff --git a/services/communication/kustomization.yaml b/services/communication/kustomization.yaml
index f161e0e..d2352b8 100644
--- a/services/communication/kustomization.yaml
+++ b/services/communication/kustomization.yaml
@@ -8,6 +8,8 @@ resources:
   - synapse-signingkey-ensure-job.yaml
   - synapse-seeder-admin-ensure-job.yaml
   - synapse-guest-appservice-secret-ensure-job.yaml
+  - guest-register-shared-secret-ensure-job.yaml
+  - synapse-guest-register-module-configmap.yaml
   - mas-configmap.yaml
   - mas-admin-client-secret-ensure-job.yaml
   - mas-deployment.yaml
diff --git a/services/communication/synapse-guest-register-module-configmap.yaml b/services/communication/synapse-guest-register-module-configmap.yaml
new file mode 100644
index 0000000..37da25d
--- /dev/null
+++ b/services/communication/synapse-guest-register-module-configmap.yaml
@@ -0,0 +1,70 @@
+# services/communication/synapse-guest-register-module-configmap.yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: synapse-guest-register-module
+data:
+  guest_register.py: |
+    import secrets
+
+    import synapse.api.auth
+    from synapse.api.errors import Codes, SynapseError
+    from synapse.http.server import DirectServeJsonResource
+    from synapse.http.servlet import parse_json_object_from_request
+
+
+    class GuestRegisterResource(DirectServeJsonResource):
+        def __init__(self, hs, shared_secret: str, header_name: str):
+            super().__init__(clock=hs.get_clock())
+            self._hs = hs
+            self._shared_secret = shared_secret
+            self._header_name = header_name
+
+        async def _async_render_POST(self, request):  # noqa: N802
+            provided = request.requestHeaders.getRawHeaders(self._header_name)
+            if not provided or not secrets.compare_digest(provided[0], self._shared_secret):
+                raise SynapseError(403, "Forbidden", errcode=Codes.FORBIDDEN)
+
+            body = parse_json_object_from_request(request)
+            initial_device_display_name = body.get("initial_device_display_name")
+            if not isinstance(initial_device_display_name, str):
+                initial_device_display_name = None
+
+            reg = self._hs.get_registration_handler()
+            address = request.getClientAddress().host
+
+            user_id = await reg.register_user(make_guest=True, address=address)
+
+            device_id = synapse.api.auth.GUEST_DEVICE_ID
+            device_id, access_token, valid_until_ms, refresh_token = await reg.register_device(
+                user_id,
+                device_id,
+                initial_device_display_name,
+                is_guest=True,
+            )
+
+            result = {
+                "user_id": user_id,
+                "device_id": device_id,
+                "access_token": access_token,
+                "home_server": self._hs.hostname,
+            }
+
+            if valid_until_ms is not None:
+                result["expires_in_ms"] = valid_until_ms - self._hs.get_clock().time_msec()
+
+            if refresh_token is not None:
+                result["refresh_token"] = refresh_token
+
+            return 200, result
+
+
+    class GuestRegisterModule:
+        def __init__(self, config, api):
+            shared_secret = config["shared_secret"]
+            header_name = config.get("header_name", "x-guest-register-secret")
+            path = config.get("path", "/_matrix/client/v3/_guest_register")
+
+            hs = api._hs  # noqa: SLF001
+            api.register_web_resource(path, GuestRegisterResource(hs, shared_secret, header_name))
+