diff --git a/.env.example b/.env.example
index 75c817a..5176ea1 100644
--- a/.env.example
+++ b/.env.example
@@ -15,14 +15,12 @@ WEB_ENABLED=true
 WEB_HOSTNAME=files.example.com
 WEB_HTTPS_PORT=443
 WEB_JWT_SECRET=ReplaceWithAtLeast32RandomBytes
-WEB_TLS_MODE=step
-STEP_CA_URL=https://ca.example.com:9000
-STEP_CA_FINGERPRINT=ReplaceWithStepRootFingerprint
-STEP_CA_PROVISIONER=fileserver
-STEP_CA_PROVISIONER_PASSWORD=ReplaceWithProvisionerPassword
-# STEP_CA_TOKEN=single-use-bootstrap-token
-# STEP_CA_PROVISIONER_PASSWORD_FILE=/run/secrets/step-ca-provisioner-password
-# STEP_CA_REBOOTSTRAP=false
+WEB_TLS_MODE=acme
+ACME_CA_SERVER=https://ca.internal/acme/acme/directory
+ACME_CA_CERTIFICATES=/state/tls/acme-ca-certificates.pem
+ACME_HTTP_LISTEN=:80
+ACME_HTTP_PORT=80
+# ACME_RENEW_CHECK_SECONDS=900
 # WEB_TLS_CERT_FILE=/state/tls/web.crt
 # WEB_TLS_KEY_FILE=/state/tls/web.key
 # WEB_JWT_TTL_SECONDS=28800
diff --git a/README.md b/README.md
index d602847..4e5df94 100644
--- a/README.md
+++ b/README.md
@@ -118,7 +118,7 @@ Run a complete disposable environment with Docker or Podman:
 The launcher builds the current application and starts an isolated, run-scoped network containing:
 
 - a real Samba AD DC for `DEV.TEST`, seeded with users, nested groups, and three `FS_*` groups;
-- a real Smallstep CA that issues the web UI certificate for `localhost`;
+- a real Smallstep CA whose ACME provisioner issues the web UI certificate for `files.localhost`;
 - an authenticated rsync daemon used by the normal backup implementation;
 - the actual file-server image, joined to the dummy domain;
 - a continuous SMB client that reads, writes, and lists files as several domain users.
@@ -126,7 +126,7 @@ The launcher builds the current application and starts an isolated, run-scoped n
 The preview starts with group, Private, FSLogix, and historical audit data. The client keeps current-day audit activity moving, while a real backup runs immediately and repeats in the background. Open the URL and use the credentials printed by the launcher. Defaults are:
 
 ```text
-URL:      https://localhost:8443
+URL:      https://files.localhost:8443
 Username: DEV\previewadmin
 Password: PreviewAdmin123!
 ```
@@ -140,8 +140,9 @@ Useful overrides:
 | Variable | Default | Purpose |
 | --- | --- | --- |
 | `DEV_HTTPS_PORT` | `8443` | HTTPS port bound to host loopback |
+| `DEV_WEB_HOSTNAME` | `files.localhost` | HTTPS name validated by the disposable ACME CA |
 | `DEV_SKIP_BUILD` | `0` | Set to `1` to reuse already-built local images |
-| `DEV_STEP_CA_IMAGE` | `docker.io/smallstep/step-ca:latest` | CA image; pin a tag or digest for reproducible CI |
+| `DEV_CA_IMAGE` | `docker.io/smallstep/step-ca:latest` | CA image; pin a tag or digest for reproducible CI |
 | `DEV_SERVER_IMAGE` | `ad-ds-simple-file-server-dev:latest` | Local file-server image name |
 | `DEV_AD_IMAGE` | `ad-ds-simple-file-server-ad-dev:latest` | Local AD/client image name |
 | `DEV_BACKUP_IMAGE` | `ad-ds-simple-file-server-backup-dev:latest` | Local rsync target image name |
@@ -209,12 +210,11 @@ The runner returns non-zero on the first failed assertion, prints bounded logs f
    - optional `BACKUP_PROGRESS_INTERVAL_SECONDS` (default `10`)
    - `WEB_HOSTNAME` (the DNS name in the HTTPS certificate)
    - optional `WEB_HTTPS_PORT` (host port, default `443`)
-   - `STEP_CA_URL`
-   - `STEP_CA_FINGERPRINT`
-   - `STEP_CA_PROVISIONER`
-   - `STEP_CA_PROVISIONER_PASSWORD`
+   - `ACME_CA_SERVER` (ACME directory URL)
+   - ACME CA root bundle (a host PEM file imported into the persistent state volume)
+   - optional `ACME_HTTP_PORT` (HTTP-01 host port, default `80`)
 
-   Setup generates a random `WEB_JWT_SECRET`. A one-time `STEP_CA_TOKEN` or a provisioner password file can be configured manually instead of keeping a provisioner password in `.env`.
+   Setup generates a random `WEB_JWT_SECRET`, stores only the generic ACME settings, and imports the public CA root as `/state/tls/acme-ca-certificates.pem`.
 
    Optional:
    - `SAMBA_HOSTNAME` (defaults to `adsambafsrv`)
@@ -301,25 +301,50 @@ The web API has no mutation endpoint other than session login/logout. Files, gro
 - Login attempts are rate-limited per client address.
 - Responses set HSTS, a restrictive Content Security Policy, clickjacking protection, MIME sniffing protection, and no-store caching.
 
-### TLS with a local Smallstep CA
+### TLS with an internal ACME CA
 
-Default enrollment uses `WEB_TLS_MODE=step`:
+The default uses standard ACME HTTP-01 enrollment. The names deliberately describe the protocol and inputs rather than a particular CA product:
 
 ```env
 WEB_ENABLED=true
 WEB_HOSTNAME=files.example.com
 WEB_HTTPS_PORT=443
 WEB_JWT_SECRET=<at-least-32-random-bytes>
-WEB_TLS_MODE=step
-STEP_CA_URL=https://ca.example.com:9000
-STEP_CA_FINGERPRINT=<root-certificate-fingerprint>
-STEP_CA_PROVISIONER=fileserver
-STEP_CA_PROVISIONER_PASSWORD=<provisioner-password>
+WEB_TLS_MODE=acme
+ACME_CA_SERVER=https://ca.internal/acme/acme/directory
+ACME_CA_CERTIFICATES=/state/tls/acme-ca-certificates.pem
+ACME_HTTP_LISTEN=:80
+ACME_HTTP_PORT=80
 ```
 
-At first startup the container bootstraps the CA root, requests a certificate for `WEB_HOSTNAME`, and stores its certificate, key, and Step client state on the persistent `state_data` volume. The `step ca renew --daemon` process renews the certificate; the HTTPS listener notices the certificate file change and reloads it.
+`ACME_CA_CERTIFICATES` is a path inside the file-server container. The setup script imports the selected host PEM bundle at the path above; manual deployments must copy or mount the bundle there. The CA must be able to resolve `WEB_HOSTNAME` and reach `http://WEB_HOSTNAME/.well-known/acme-challenge/...` on port 80. `ACME_HTTP_LISTEN` controls the in-container standalone challenge listener and `ACME_HTTP_PORT` controls the Compose host-port mapping.
 
-For secret-file based enrollment, set `STEP_CA_PROVISIONER_PASSWORD_FILE` to a mounted file. A single-use `STEP_CA_TOKEN` is also supported. To use externally managed files instead:
+The equivalent Traefik settings translate as follows:
+
+| Traefik setting | File-server setting |
+| --- | --- |
+| `acme.httpchallenge=true` | `WEB_TLS_MODE=acme` |
+| `acme.httpchallenge.entrypoint=http` | `ACME_HTTP_LISTEN=:80` and `ACME_HTTP_PORT=80` |
+| `acme.caserver=https://ca.internal/acme/acme/directory` | `ACME_CA_SERVER=https://ca.internal/acme/acme/directory` |
+| `acme.cacertificates=/traefik/stepca/roots.pem` | `ACME_CA_CERTIFICATES=<the mounted PEM path inside this container>` |
+
+The client uses [`step ca certificate --acme --root --standalone`](https://smallstep.com/docs/step-cli/reference/ca/certificate/) and periodically checks whether the certificate needs renewal. Renewal is a fresh ACME order, so this mode is not coupled to a proprietary renewal endpoint. The HTTPS listener reloads the replaced certificate files.
+
+A generic direct-CA/JWK or token enrollment mode remains available when ACME HTTP-01 cannot be routed:
+
+```env
+WEB_TLS_MODE=ca
+TLS_CA_URL=https://ca.internal:9000
+TLS_CA_FINGERPRINT=<root-certificate-fingerprint>
+TLS_CA_PROVISIONER=fileserver
+TLS_CA_PROVISIONER_PASSWORD=<provisioner-password>
+# TLS_CA_PROVISIONER_PASSWORD_FILE=/run/secrets/ca-provisioner-password
+# TLS_CA_TOKEN=<single-use-bootstrap-token>
+# TLS_CA_REBOOTSTRAP=false
+# TLS_CA_STATE_DIR=/state/tls-client
+```
+
+Externally managed certificate files can be used instead:
 
 ```env
 WEB_TLS_MODE=files
@@ -327,12 +352,12 @@ WEB_TLS_CERT_FILE=/state/tls/web.crt
 WEB_TLS_KEY_FILE=/state/tls/web.key
 ```
 
-Smallstep trust configuration is reused from the state volume on normal restarts, so a temporary CA outage does not stop Samba or an already-certificate-equipped web service. Set `STEP_CA_REBOOTSTRAP=true` only when intentionally replacing the configured CA trust.
-
 Useful optional settings:
 
 | Variable | Default | Purpose |
 | --- | ---: | --- |
+| `WEB_TLS_AUTORENEW` | `true` | Renew managed certificates automatically |
+| `ACME_RENEW_CHECK_SECONDS` | `900` | Interval for ACME renewal checks; minimum 60 seconds |
 | `WEB_JWT_TTL_SECONDS` | `28800` | Session lifetime, 5 minutes to 7 days |
 | `WEB_LOGIN_ATTEMPTS_PER_5_MIN` | `10` | Per-address login attempt limit |
 | `WEB_USAGE_SCAN_INTERVAL_SECONDS` | `900` | Recursive storage scan interval |
diff --git a/app/init.sh b/app/init.sh
index 390d3fb..f67d282 100755
--- a/app/init.sh
+++ b/app/init.sh
@@ -303,7 +303,8 @@ web_should_start() {
     env_is_true "$WEB_ENABLED"
     return
   fi
-  if [[ -n "${STEP_CA_URL:-}" ]] || \
+  if [[ -n "${ACME_CA_SERVER:-}" ]] || \
+     [[ -n "${TLS_CA_URL:-}" ]] || \
      [[ -s "${WEB_TLS_CERT_FILE:-/state/tls/web.crt}" ]]; then
     return 0
   fi
@@ -328,17 +329,57 @@ ensure_web_jwt_secret() {
   log 'WEB_JWT_SECRET was not provided; using a persistent generated secret.'
 }
 
+selected_tls_mode() {
+  case "${WEB_TLS_MODE:-}" in
+    '')
+      if [[ -n "${ACME_CA_SERVER:-}" ]]; then
+        printf 'acme'
+      else
+        printf 'ca'
+      fi
+      ;;
+    acme|ca|files) printf '%s' "$WEB_TLS_MODE" ;;
+    *) return 1 ;;
+  esac
+}
+
+request_acme_certificate() {
+  local cert_tmp="${WEB_TLS_CERT_FILE}.acme.tmp"
+  local key_tmp="${WEB_TLS_KEY_FILE}.acme.tmp"
+
+  rm -f "$cert_tmp" "$key_tmp"
+  log "Requesting ACME HTTPS certificate for ${WEB_HOSTNAME}"
+  if ! step ca certificate "$WEB_HOSTNAME" "$cert_tmp" "$key_tmp" \
+    --acme "$ACME_CA_SERVER" \
+    --root "$ACME_CA_CERTIFICATES" \
+    --standalone \
+    --http-listen "${ACME_HTTP_LISTEN:-:80}" \
+    --force; then
+    rm -f "$cert_tmp" "$key_tmp"
+    return 1
+  fi
+
+  chmod 0600 "$key_tmp"
+  chmod 0644 "$cert_tmp"
+  mv -f "$key_tmp" "$WEB_TLS_KEY_FILE"
+  mv -f "$cert_tmp" "$WEB_TLS_CERT_FILE"
+}
+
 configure_web_tls() {
-  local tls_mode="${WEB_TLS_MODE:-step}"
-  local tls_dir=""
+  local tls_mode=""
   local provisioner_password_file=""
 
+  if ! tls_mode="$(selected_tls_mode)"; then
+    printf '[init] ERROR: WEB_TLS_MODE must be acme, ca, or files\n' >&2
+    return 1
+  fi
+  export ACTIVE_WEB_TLS_MODE="$tls_mode"
   export WEB_HOSTNAME="${WEB_HOSTNAME:-${AD_DNS_NAME}}"
   export WEB_BIND_PORT="${WEB_BIND_PORT:-8443}"
   export WEB_TLS_CERT_FILE="${WEB_TLS_CERT_FILE:-/state/tls/web.crt}"
   export WEB_TLS_KEY_FILE="${WEB_TLS_KEY_FILE:-/state/tls/web.key}"
-  tls_dir="$(dirname "$WEB_TLS_CERT_FILE")"
-  mkdir -p "$tls_dir" "$(dirname "$WEB_TLS_KEY_FILE")"
+  export STEPPATH="${TLS_CA_STATE_DIR:-/state/tls-client}"
+  mkdir -p "$(dirname "$WEB_TLS_CERT_FILE")" "$(dirname "$WEB_TLS_KEY_FILE")" "$STEPPATH"
 
   if [[ "$tls_mode" == "files" ]]; then
     if [[ ! -s "$WEB_TLS_CERT_FILE" || ! -s "$WEB_TLS_KEY_FILE" ]]; then
@@ -347,41 +388,49 @@ configure_web_tls() {
     fi
     return
   fi
-  if [[ "$tls_mode" != "step" ]]; then
-    printf '[init] ERROR: WEB_TLS_MODE must be step or files\n' >&2
-    return 1
+
+  if [[ "$tls_mode" == "acme" ]]; then
+    require_env ACME_CA_SERVER
+    require_env ACME_CA_CERTIFICATES
+    if [[ ! -s "$ACME_CA_CERTIFICATES" ]]; then
+      printf '[init] ERROR: ACME_CA_CERTIFICATES is not a readable PEM bundle: %s\n' "$ACME_CA_CERTIFICATES" >&2
+      return 1
+    fi
+    if [[ ! -s "$WEB_TLS_CERT_FILE" || ! -s "$WEB_TLS_KEY_FILE" ]]; then
+      request_acme_certificate
+    fi
+    return
   fi
 
-  export STEPPATH="${STEP_PATH:-/state/step}"
   if [[ ! -s "$STEPPATH/config/defaults.json" ]] || \
-     env_is_true "${STEP_CA_REBOOTSTRAP:-false}"; then
-    require_env STEP_CA_URL
-    require_env STEP_CA_FINGERPRINT
-    log "Bootstrapping Smallstep trust for ${STEP_CA_URL}"
-    step ca bootstrap --force --ca-url "$STEP_CA_URL" --fingerprint "$STEP_CA_FINGERPRINT"
+     env_is_true "${TLS_CA_REBOOTSTRAP:-false}"; then
+    require_env TLS_CA_URL
+    require_env TLS_CA_FINGERPRINT
+    log "Bootstrapping CA trust for ${TLS_CA_URL}"
+    step ca bootstrap --force --ca-url "$TLS_CA_URL" --fingerprint "$TLS_CA_FINGERPRINT"
   fi
 
   if [[ ! -s "$WEB_TLS_CERT_FILE" || ! -s "$WEB_TLS_KEY_FILE" ]]; then
     log "Requesting HTTPS certificate for ${WEB_HOSTNAME}"
-    if [[ -n "${STEP_CA_TOKEN:-}" ]]; then
-      step ca certificate "$WEB_HOSTNAME" "$WEB_TLS_CERT_FILE" "$WEB_TLS_KEY_FILE" --token "$STEP_CA_TOKEN" --force
+    if [[ -n "${TLS_CA_TOKEN:-}" ]]; then
+      step ca certificate "$WEB_HOSTNAME" "$WEB_TLS_CERT_FILE" "$WEB_TLS_KEY_FILE" --token "$TLS_CA_TOKEN" --force
     else
-      require_env STEP_CA_PROVISIONER
-      if [[ -n "${STEP_CA_PROVISIONER_PASSWORD_FILE:-}" ]]; then
-        provisioner_password_file="$STEP_CA_PROVISIONER_PASSWORD_FILE"
-      elif [[ -n "${STEP_CA_PROVISIONER_PASSWORD:-}" ]]; then
-        provisioner_password_file="/run/step-provisioner-password"
+      require_env TLS_CA_PROVISIONER
+      if [[ -n "${TLS_CA_PROVISIONER_PASSWORD_FILE:-}" ]]; then
+        provisioner_password_file="$TLS_CA_PROVISIONER_PASSWORD_FILE"
+      elif [[ -n "${TLS_CA_PROVISIONER_PASSWORD:-}" ]]; then
+        provisioner_password_file="/run/tls-ca-provisioner-password"
         umask 077
-        printf '%s\n' "$STEP_CA_PROVISIONER_PASSWORD" > "$provisioner_password_file"
+        printf '%s\n' "$TLS_CA_PROVISIONER_PASSWORD" > "$provisioner_password_file"
       else
-        printf '[init] ERROR: STEP_CA_TOKEN, STEP_CA_PROVISIONER_PASSWORD_FILE, or STEP_CA_PROVISIONER_PASSWORD is required for initial TLS setup\n' >&2
+        printf '[init] ERROR: TLS_CA_TOKEN, TLS_CA_PROVISIONER_PASSWORD_FILE, or TLS_CA_PROVISIONER_PASSWORD is required for initial TLS setup\n' >&2
         return 1
       fi
       step ca certificate "$WEB_HOSTNAME" "$WEB_TLS_CERT_FILE" "$WEB_TLS_KEY_FILE" \
-        --provisioner "$STEP_CA_PROVISIONER" \
+        --provisioner "$TLS_CA_PROVISIONER" \
         --provisioner-password-file "$provisioner_password_file" \
         --force
-      if [[ "$provisioner_password_file" == "/run/step-provisioner-password" ]]; then
+      if [[ "$provisioner_password_file" == "/run/tls-ca-provisioner-password" ]]; then
         rm -f "$provisioner_password_file"
       fi
     fi
@@ -390,6 +439,24 @@ configure_web_tls() {
   chmod 0644 "$WEB_TLS_CERT_FILE"
 }
 
+start_acme_renewal_daemon() {
+  local interval="${ACME_RENEW_CHECK_SECONDS:-900}"
+  if [[ ! "$interval" =~ ^[0-9]+$ ]] || (( interval < 60 )); then
+    log "Invalid ACME_RENEW_CHECK_SECONDS=${interval}; using 900"
+    interval=900
+  fi
+
+  log "Starting ACME certificate renewal check every ${interval} seconds"
+  (
+    while true; do
+      sleep "$interval"
+      if step certificate needs-renewal "$WEB_TLS_CERT_FILE" >/dev/null 2>&1; then
+        request_acme_certificate || log 'ACME certificate renewal failed; retrying at the next interval.'
+      fi
+    done
+  ) &
+}
+
 start_observability_services() {
   log 'Starting Samba audit collector'
   python3 /app/audit_collector.py &
@@ -397,10 +464,15 @@ start_observability_services() {
   if web_should_start; then
     ensure_web_jwt_secret
     configure_web_tls
-    unset STEP_CA_PROVISIONER_PASSWORD STEP_CA_TOKEN
-    if [[ "${WEB_TLS_MODE:-step}" == "step" ]] && env_is_true "${WEB_TLS_AUTORENEW:-true}"; then
-      log 'Starting Smallstep certificate renewal daemon'
-      step ca renew --daemon --force "$WEB_TLS_CERT_FILE" "$WEB_TLS_KEY_FILE" &
+    unset TLS_CA_PROVISIONER_PASSWORD TLS_CA_TOKEN
+    if env_is_true "${WEB_TLS_AUTORENEW:-true}"; then
+      case "$ACTIVE_WEB_TLS_MODE" in
+        acme) start_acme_renewal_daemon ;;
+        ca)
+          log 'Starting CA certificate renewal daemon'
+          step ca renew --daemon --force "$WEB_TLS_CERT_FILE" "$WEB_TLS_KEY_FILE" &
+          ;;
+      esac
     fi
     log "Starting read-only web UI for https://${WEB_HOSTNAME}"
     python3 /app/web_ui.py &
diff --git a/dev/e2e.py b/dev/e2e.py
index 6734955..a4c0e29 100755
--- a/dev/e2e.py
+++ b/dev/e2e.py
@@ -30,8 +30,23 @@ DOMAIN_SID = os.environ["PREVIEW_DOMAIN_SID"]
 ADMIN_USER = os.environ["PREVIEW_ADMIN_USER"]
 ADMIN_PASSWORD = os.environ["PREVIEW_ADMIN_PASSWORD"]
 USER_PASSWORD = os.environ["PREVIEW_USER_PASSWORD"]
-BASE_URL = f"https://localhost:{HTTPS_PORT}"
+HTTPS_HOST = os.environ["PREVIEW_HTTPS_HOST"]
+BASE_URL = f"https://{HTTPS_HOST}:{HTTPS_PORT}"
+_ORIGINAL_GETADDRINFO = socket.getaddrinfo
+
+
+def preview_getaddrinfo(host, port, *args, **kwargs):
+    if host == HTTPS_HOST:
+        host = "127.0.0.1"
+    return _ORIGINAL_GETADDRINFO(host, port, *args, **kwargs)
+
+
+socket.getaddrinfo = preview_getaddrinfo
 TLS_CONTEXT = ssl.create_default_context(cafile=CA_ROOT)
+HTTP_OPENER = urllib.request.build_opener(
+    urllib.request.ProxyHandler({}),
+    urllib.request.HTTPSHandler(context=TLS_CONTEXT),
+)
 
 
 @dataclass
@@ -85,9 +100,7 @@ def http(
         f"{BASE_URL}{path}", data=body, headers=headers, method=method
     )
     try:
-        with urllib.request.urlopen(
-            request, context=TLS_CONTEXT, timeout=30
-        ) as response:
+        with HTTP_OPENER.open(request, timeout=30) as response:
             return Response(response.status, response.headers, response.read())
     except urllib.error.HTTPError as exc:
         return Response(exc.code, exc.headers, exc.read())
@@ -152,10 +165,10 @@ def main() -> int:
     check("max-age=" in index.headers.get("Strict-Transport-Security", ""), "HSTS missing")
     check("default-src 'self'" in index.headers.get("Content-Security-Policy", ""), "CSP missing")
     with socket.create_connection(("localhost", HTTPS_PORT), timeout=10) as raw:
-        with TLS_CONTEXT.wrap_socket(raw, server_hostname="localhost") as secured:
+        with TLS_CONTEXT.wrap_socket(raw, server_hostname=HTTPS_HOST) as secured:
             certificate = secured.getpeercert()
     sans = {value for kind, value in certificate.get("subjectAltName", ()) if kind == "DNS"}
-    check("localhost" in sans, "issued certificate does not cover localhost")
+    check(HTTPS_HOST in sans, f"issued certificate does not cover {HTTPS_HOST}")
     check(certificate.get("issuer") != certificate.get("subject"), "web certificate is self-signed instead of CA-issued")
 
     announce("JWT boundary, real Kerberos credentials, and Domain Admin authorization")
diff --git a/docker-compose.yml b/docker-compose.yml
index 0b7c901..7ca25d9 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -13,6 +13,7 @@ services:
     ports:
       - "445:445"
       - "139:139"
+      - "${ACME_HTTP_PORT:-80}:80"
       - "${WEB_HTTPS_PORT:-443}:${WEB_BIND_PORT:-8443}"
     volumes:
       - private_data:/data/private
diff --git a/scripts/dev b/scripts/dev
index 7d95b22..9f9d74b 100755
--- a/scripts/dev
+++ b/scripts/dev
@@ -34,6 +34,7 @@ dev_realm=${DEV_REALM:-DEV.TEST}
 dev_workgroup=${DEV_WORKGROUP:-DEV}
 dev_dns_domain=${DEV_DNS_DOMAIN:-dev.test}
 dev_base_dn=${DEV_BASE_DN:-DC=dev,DC=test}
+dev_web_hostname=${DEV_WEB_HOSTNAME:-files.localhost}
 dev_dc_password=${DEV_DC_PASSWORD:-PreviewDc123!}
 dev_user_password=${DEV_USER_PASSWORD:-PreviewUser123!}
 dev_admin_user=${DEV_ADMIN_USER:-previewadmin}
@@ -49,7 +50,7 @@ dev_backup_interval=${DEV_BACKUP_INTERVAL_SECONDS:-120}
 server_image=${DEV_SERVER_IMAGE:-ad-ds-simple-file-server-dev:latest}
 ad_image=${DEV_AD_IMAGE:-ad-ds-simple-file-server-ad-dev:latest}
 backup_image=${DEV_BACKUP_IMAGE:-ad-ds-simple-file-server-backup-dev:latest}
-step_ca_image=${DEV_STEP_CA_IMAGE:-docker.io/smallstep/step-ca:latest}
+ca_image=${DEV_CA_IMAGE:-docker.io/smallstep/step-ca:latest}
 
 run_id="ad-file-server-dev-$$-$RANDOM"
 network_name="$run_id-net"
@@ -216,18 +217,20 @@ for volume in "${volumes[@]}"; do
   "$engine" volume create "$volume" >/dev/null
 done
 
-printf 'starting local CA: %s\n' "$step_ca_image"
+printf 'starting local CA: %s\n' "$ca_image"
 "$engine" run -d \
   --name "$ca_container" \
   --hostname "ca.${dev_dns_domain}" \
   --network "$network_name" \
   --ip "$ca_ip" \
+  --add-host "${dev_web_hostname}:${files_ip}" \
   -e "DOCKER_STEPCA_INIT_NAME=AD file server preview CA" \
   -e "DOCKER_STEPCA_INIT_DNS_NAMES=ca.${dev_dns_domain},localhost,127.0.0.1" \
   -e "DOCKER_STEPCA_INIT_PROVISIONER_NAME=${dev_ca_provisioner}" \
   -e "DOCKER_STEPCA_INIT_PASSWORD=${dev_ca_password}" \
+  -e "DOCKER_STEPCA_INIT_ACME=true" \
   -v "$ca_volume:/home/step" \
-  "$step_ca_image" >/dev/null
+  "$ca_image" >/dev/null
 
 if ! wait_for_exec "$ca_container" 120 step ca health \
   --ca-url=https://localhost:9000 \
@@ -235,11 +238,15 @@ if ! wait_for_exec "$ca_container" 120 step ca health \
   show_logs
   die 'local CA did not become healthy'
 fi
-ca_fingerprint=$("$engine" exec "$ca_container" step certificate fingerprint \
-  /home/step/certs/root_ca.crt)
 preview_tmp_root=${TMPDIR:-/tmp}
 ca_root_file="${preview_tmp_root%/}/${run_id}-root-ca.crt"
 "$engine" exec "$ca_container" cat /home/step/certs/root_ca.crt > "$ca_root_file"
+"$engine" run --rm -i \
+  -v "$state_volume:/state" \
+  --entrypoint /bin/bash \
+  "$server_image" -lc \
+  'install -d -m 0755 /state/tls && dd of=/state/tls/acme-ca-certificates.pem status=none && chmod 0644 /state/tls/acme-ca-certificates.pem' \
+  < "$ca_root_file"
 
 printf 'starting disposable rsync backup target\n'
 "$engine" run -d \
@@ -312,14 +319,13 @@ printf 'starting actual file server and HTTPS web UI\n'
   -e "NETBIOS_NAME=FILES" \
   -e "AD_DNS_NAME=files.${dev_dns_domain}" \
   -e "WEB_ENABLED=true" \
-  -e "WEB_HOSTNAME=localhost" \
+  -e "WEB_HOSTNAME=${dev_web_hostname}" \
   -e "WEB_BIND_PORT=8443" \
   -e "WEB_JWT_SECRET=preview-only-jwt-secret-with-at-least-32-bytes" \
-  -e "WEB_TLS_MODE=step" \
-  -e "STEP_CA_URL=https://ca.${dev_dns_domain}:9000" \
-  -e "STEP_CA_FINGERPRINT=${ca_fingerprint}" \
-  -e "STEP_CA_PROVISIONER=${dev_ca_provisioner}" \
-  -e "STEP_CA_PROVISIONER_PASSWORD=${dev_ca_password}" \
+  -e "WEB_TLS_MODE=acme" \
+  -e "ACME_CA_SERVER=https://ca.${dev_dns_domain}:9000/acme/acme/directory" \
+  -e "ACME_CA_CERTIFICATES=/state/tls/acme-ca-certificates.pem" \
+  -e "ACME_HTTP_LISTEN=:80" \
   -e "WEB_USAGE_SCAN_INTERVAL_SECONDS=60" \
   -e "WEB_DIRECTORY_CACHE_SECONDS=30" \
   -e "AUDIT_POLL_SECONDS=0.25" \
@@ -387,6 +393,7 @@ if [[ $run_e2e == 1 ]]; then
     PREVIEW_BACKUP_CONTAINER="$backup_container" \
     PREVIEW_CA_ROOT="$ca_root_file" \
     PREVIEW_HTTPS_PORT="$dev_https_port" \
+    PREVIEW_HTTPS_HOST="$dev_web_hostname" \
     PREVIEW_REALM="$dev_realm" \
     PREVIEW_WORKGROUP="$dev_workgroup" \
     PREVIEW_DNS_DOMAIN="$dev_dns_domain" \
@@ -402,7 +409,7 @@ if [[ $run_e2e == 1 ]]; then
 fi
 
 printf '\nPreview ready\n'
-printf '  URL:      https://localhost:%s\n' "$dev_https_port"
+printf '  URL:      https://%s:%s\n' "$dev_web_hostname" "$dev_https_port"
 printf '  Username: %s\\%s\n' "$dev_workgroup" "$dev_admin_user"
 printf '  Password: %s\n' "$dev_admin_password"
 printf '  CA root:  %s\n' "$ca_root_file"
diff --git a/setup b/setup
index 8c010bc..f4b1641 100755
--- a/setup
+++ b/setup
@@ -138,10 +138,11 @@ write_env_file() {
   local web_hostname=""
   local web_https_port="443"
   local web_jwt_secret=""
-  local step_ca_url=""
-  local step_ca_fingerprint=""
-  local step_ca_provisioner=""
-  local step_ca_provisioner_password=""
+  local acme_ca_server=""
+  local acme_ca_certificates_source=""
+  local acme_ca_certificates_source_dir=""
+  local acme_http_port="80"
+  local acme_http_port_input=""
   local web_hostname_input=""
   local service_account_sam=""
   local fslogix_group_prompt=""
@@ -217,10 +218,16 @@ write_env_file() {
   web_hostname="${web_hostname_input:-$web_hostname}"
   read -r -p "WEB_HTTPS_PORT [443]: " web_https_port
   web_https_port="${web_https_port:-443}"
-  prompt_value step_ca_url "STEP_CA_URL (e.g. https://ca.example.com:9000)"
-  prompt_value step_ca_fingerprint "STEP_CA_FINGERPRINT"
-  prompt_value step_ca_provisioner "STEP_CA_PROVISIONER (JWK provisioner name)"
-  prompt_value step_ca_provisioner_password "STEP_CA_PROVISIONER_PASSWORD" true
+  prompt_value acme_ca_server "ACME_CA_SERVER (e.g. https://ca.internal/acme/acme/directory)"
+  prompt_value acme_ca_certificates_source "ACME CA root bundle (PEM file on this host)"
+  if [[ ! -s "$acme_ca_certificates_source" ]]; then
+    printf "ACME CA root bundle is not a readable file: %s\n" "$acme_ca_certificates_source" >&2
+    return 1
+  fi
+  acme_ca_certificates_source_dir="$(cd "$(dirname "$acme_ca_certificates_source")" && pwd)"
+  acme_ca_certificates_source="${acme_ca_certificates_source_dir}/$(basename "$acme_ca_certificates_source")"
+  read -r -p "ACME_HTTP_PORT (HTTP-01 host port) [80]: " acme_http_port_input
+  acme_http_port="${acme_http_port_input:-80}"
 
   web_jwt_secret="$(python3 - <<'PY'
 import secrets
@@ -279,11 +286,11 @@ WEB_ENABLED=true
 WEB_HOSTNAME=${web_hostname}
 WEB_HTTPS_PORT=${web_https_port}
 WEB_JWT_SECRET=${web_jwt_secret}
-WEB_TLS_MODE=step
-STEP_CA_URL=${step_ca_url}
-STEP_CA_FINGERPRINT=${step_ca_fingerprint}
-STEP_CA_PROVISIONER=${step_ca_provisioner}
-STEP_CA_PROVISIONER_PASSWORD=${step_ca_provisioner_password}
+WEB_TLS_MODE=acme
+ACME_CA_SERVER=${acme_ca_server}
+ACME_CA_CERTIFICATES=/state/tls/acme-ca-certificates.pem
+ACME_HTTP_LISTEN=:80
+ACME_HTTP_PORT=${acme_http_port}
 EOF
 
   cp "$BOOTSTRAP_ENV_FILE" "$ENV_FILE"
@@ -293,6 +300,12 @@ EOF
   printf "Building image...\n"
   docker compose build samba
 
+  printf "Importing ACME CA root bundle...\n"
+  docker compose run --rm --no-deps -T \
+    --entrypoint /bin/bash samba -lc \
+    'install -d -m 0755 "$(dirname "$ACME_CA_CERTIFICATES")" && dd of="$ACME_CA_CERTIFICATES" status=none && chmod 0644 "$ACME_CA_CERTIFICATES"' \
+    < "$acme_ca_certificates_source"
+
   printf "Provisioning service account %s...\n" "$SERVICE_ACCOUNT_NAME"
   docker compose run --rm --entrypoint /bin/bash samba -lc '
 set -euo pipefail
@@ -348,11 +361,11 @@ WEB_ENABLED=true
 WEB_HOSTNAME=${web_hostname}
 WEB_HTTPS_PORT=${web_https_port}
 WEB_JWT_SECRET=${web_jwt_secret}
-WEB_TLS_MODE=step
-STEP_CA_URL=${step_ca_url}
-STEP_CA_FINGERPRINT=${step_ca_fingerprint}
-STEP_CA_PROVISIONER=${step_ca_provisioner}
-STEP_CA_PROVISIONER_PASSWORD=${step_ca_provisioner_password}
+WEB_TLS_MODE=acme
+ACME_CA_SERVER=${acme_ca_server}
+ACME_CA_CERTIFICATES=/state/tls/acme-ca-certificates.pem
+ACME_HTTP_LISTEN=:80
+ACME_HTTP_PORT=${acme_http_port}
 # Optional overrides:
 # LDAP_URI=ldaps://${domain}
 # LDAP_BASE_DN=DC=example,DC=com
@@ -375,7 +388,7 @@ STEP_CA_PROVISIONER_PASSWORD=${step_ca_provisioner_password}
 # WEB_DIRECTORY_CACHE_SECONDS=300
 # AUDIT_COMPRESS_AFTER_HOURS=24
 # AUDIT_QUERY_MAX_DAYS=31
-# STEP_CA_PROVISIONER_PASSWORD_FILE=/run/secrets/step-ca-provisioner-password
+# ACME_RENEW_CHECK_SECONDS=900
 # WEB_TLS_CERT_FILE=/state/tls/web.crt
 # WEB_TLS_KEY_FILE=/state/tls/web.key
 EOF