diff --git a/docs/dev/rest-api/authentication.md b/docs/dev/rest-api/authentication.md
index 831050b3..0f707182 100644
--- a/docs/dev/rest-api/authentication.md
+++ b/docs/dev/rest-api/authentication.md
@@ -299,7 +299,7 @@ With `--caddy`, unshackle also starts `caddy run` using the `Caddyfile` located
 
 The header and config are identical between modes, but the code that enforces them differs:
 
-- **API-only server** (`--api-only`, or `--remote-only` which forces API-only). An `api_key_authentication` middleware runs on every request. It lets `GET /api/health` through unconditionally, then reads `X-Secret-Key`. An empty header returns the *"Secret Key is Empty."* body; a header that is not a configured user returns *"Secret Key is Invalid."*. In this mode the accepted-keys map contains exactly one entry: your `api_secret` (labelled `api_user`, with no devices). With `--no-key`, this middleware is simply not installed and the users map is empty.
+- **API-only server** (`--api-only`, or `--remote-only` which forces API-only). An `api_key_authentication` middleware runs on every request. It lets `GET /api/health` through unconditionally, then reads `X-Secret-Key`. An empty header returns the *"Secret Key is Empty."* body; a header that is not a configured user returns *"Secret Key is Invalid."*. In this mode the accepted-keys map holds your `api_secret` (labelled `api_user`, with no devices) plus every key under `serve.users`, so a per-user key authenticates here exactly as it does on the integrated server, and that user's `services` allowlist applies as usual. With `--no-key`, this middleware is simply not installed and the users map is empty.
 
 - **Integrated server** (default). A `serve_authentication` middleware wraps pywidevine's authentication (and pyplayready's for `/playready*` paths), and the REST routes live in the same application, guarded by the same check. Here the accepted-keys map is your full `serve` config: `api_secret` (auto-added with access to all loaded devices) plus every entry under `users`, each with its declared `devices` / `playready_devices`.
 
diff --git a/docs/reference/configuration/services.md b/docs/reference/configuration/services.md
index 3ba1043a..95ee8ff8 100644
--- a/docs/reference/configuration/services.md
+++ b/docs/reference/configuration/services.md
@@ -82,9 +82,18 @@ keep auth tokens in localStorage rather than in HTTP cookies need. Extraction is
 
 Definitions of remote unshackle service servers, used by the `--remote` mode. Each entry is
 named by you (pick it with `--server`, or omit that flag when only one is configured) and gives
-the server's `url` (required), an optional `api_key` sent as `X-Secret-Key`, an optional
-`server_cdm` boolean, and an optional `services` sub-dict of per-service local overrides such
-as `title_map`. In `--remote` mode unshackle turns the server's service list into synthetic CLI
+the server's `url` (required), an optional `api_key`, an optional `auth_headers` list, an
+optional `server_cdm` boolean, and an optional `services` sub-dict of per-service local
+overrides such as `title_map`.
+
+`auth_headers` lists extra header names to send the API key in, tried before the defaults
+`X-Secret-Key` and `X-Api-Key`, which are always appended as fallbacks. unshackle sends the
+first name; if the server answers `401`, it retries the same request with the next name, and
+keeps the one that works for the rest of the session. Names you list keep your spelling and are
+not repeated in the fallbacks, so `auth_headers: ["Authorization", "x-secret-key"]` is tried as
+`Authorization`, `x-secret-key`, `X-Api-Key`.
+
+In `--remote` mode unshackle turns the server's service list into synthetic CLI
 commands that run against it, falling back to the tags in that `services` sub-dict when the
 list cannot be fetched. See [remote sessions](../../dev/rest-api/remote-sessions.md) for the
 full setup.
diff --git a/tests/remote/unit/test_remote_client.py b/tests/remote/unit/test_remote_client.py
index 4f6ef202..9ee379d9 100644
--- a/tests/remote/unit/test_remote_client.py
+++ b/tests/remote/unit/test_remote_client.py
@@ -85,6 +85,65 @@ def test_4xx_raises_systemexit_with_logged_error(client: RemoteClient, caplog: p
     assert "no such session" in caplog.text
 
 
+@responses.activate
+def test_401_falls_back_to_next_auth_header(client: RemoteClient) -> None:
+    seen: list[tuple[str | None, str | None]] = []
+
+    def cb(request):
+        seen.append((request.headers.get("X-Secret-Key"), request.headers.get("X-Api-Key")))
+        if request.headers.get("X-Api-Key") == "secret-xyz":
+            return (200, {}, json.dumps({"status": "ok"}))
+        return (401, {}, json.dumps({"message": "Secret Key is Invalid."}))
+
+    responses.add_callback(responses.GET, "http://srv:8786/api/services", callback=cb)
+
+    assert client.get("/api/services") == {"status": "ok"}
+    assert seen == [("secret-xyz", None), (None, "secret-xyz")]
+
+    # the winning header is sticky: no second attempt on the next request
+    seen.clear()
+    assert client.get("/api/services") == {"status": "ok"}
+    assert seen == [(None, "secret-xyz")]
+
+
+@responses.activate
+def test_non_401_error_does_not_fall_back(client: RemoteClient, caplog: pytest.LogCaptureFixture) -> None:
+    responses.add(
+        responses.GET,
+        "http://srv:8786/api/services",
+        json={"error_code": "FORBIDDEN", "message": "nope"},
+        status=403,
+    )
+    with caplog.at_level("ERROR"), pytest.raises(SystemExit):
+        client.get("/api/services")
+    assert len(responses.calls) == 1
+    assert client.session.headers.get("X-Secret-Key") == "secret-xyz"
+
+
+@responses.activate
+def test_401_on_every_header_exits(client: RemoteClient, caplog: pytest.LogCaptureFixture) -> None:
+    responses.add(
+        responses.GET,
+        "http://srv:8786/api/services",
+        json={"error_code": "UNAUTHORIZED", "message": "Secret Key is Invalid."},
+        status=401,
+    )
+    with caplog.at_level("ERROR"), pytest.raises(SystemExit):
+        client.get("/api/services")
+    assert len(responses.calls) == 2
+    assert "Secret Key is Invalid." in caplog.text
+
+
+@responses.activate
+def test_single_configured_auth_header_does_not_retry() -> None:
+    c = RemoteClient(server_url="http://srv:8786", api_key="k", auth_headers=["X-Api-Key"])
+    responses.add(responses.GET, "http://srv:8786/api/services", json={"message": "nope"}, status=401)
+    with pytest.raises(SystemExit):
+        c.get("/api/services")
+    assert len(responses.calls) == 1
+    assert c.session.headers.get("X-Api-Key") == "k"
+
+
 @responses.activate
 def test_connection_error_raises_systemexit(client: RemoteClient) -> None:
     import requests
diff --git a/tests/remote/unit/test_remote_resolve.py b/tests/remote/unit/test_remote_resolve.py
index ae31e77b..5d264a32 100644
--- a/tests/remote/unit/test_remote_resolve.py
+++ b/tests/remote/unit/test_remote_resolve.py
@@ -49,6 +49,43 @@ def multi_remote_services(monkeypatch: pytest.MonkeyPatch) -> None:
     )
 
 
+def test_resolve_server_default_auth_headers(single_remote_service) -> None:
+    _, _, services = resolve_server("primary")
+    assert services["_auth_headers"] == ["X-Secret-Key", "X-Api-Key"]
+
+
+def test_resolve_server_custom_auth_headers_extend_defaults(monkeypatch: pytest.MonkeyPatch) -> None:
+    from unshackle.core import remote_service as rs
+
+    monkeypatch.setattr(
+        rs.config, "remote_services", {"p": {"url": "https://p:8080", "auth_headers": ["Authorization"]}}
+    )
+    _, _, services = resolve_server("p")
+    assert services["_auth_headers"] == ["Authorization", "X-Secret-Key", "X-Api-Key"]
+
+
+def test_resolve_server_auth_headers_dedup_is_case_insensitive(monkeypatch: pytest.MonkeyPatch) -> None:
+    from unshackle.core import remote_service as rs
+
+    monkeypatch.setattr(
+        rs.config,
+        "remote_services",
+        {"p": {"url": "https://p:8080", "auth_headers": ["Authorization", "x-secret-key"]}},
+    )
+    _, _, services = resolve_server("p")
+    assert services["_auth_headers"] == ["Authorization", "x-secret-key", "X-Api-Key"]
+
+
+@pytest.mark.parametrize("bad", ["X-Api-Key", [], [""], ["X-Api-Key", 3]])
+def test_resolve_server_bad_auth_headers_raises(monkeypatch: pytest.MonkeyPatch, bad: object) -> None:
+    from unshackle.core import remote_service as rs
+
+    monkeypatch.setattr(rs.config, "remote_services", {"p": {"url": "https://p:8080", "auth_headers": bad}})
+    with pytest.raises(click.ClickException) as exc:
+        resolve_server("p")
+    assert "auth_headers" in str(exc.value.message)
+
+
 def test_resolve_server_no_config_raises_click(empty_remote_services) -> None:
     with pytest.raises(click.ClickException) as exc:
         resolve_server(None)
diff --git a/tests/remote/unit/test_serve_cli.py b/tests/remote/unit/test_serve_cli.py
index 5ae0165c..55bc61a4 100644
--- a/tests/remote/unit/test_serve_cli.py
+++ b/tests/remote/unit/test_serve_cli.py
@@ -69,6 +69,61 @@ def test_serve_no_key_without_api_secret_does_not_require_secret(
     assert result.exit_code == 0, result.output
 
 
+async def test_api_only_accepts_serve_users_keys(
+    runner: CliRunner, monkeypatch: pytest.MonkeyPatch, aiohttp_client
+) -> None:
+    """In api-only keyed mode the accepted keys are api_secret plus every `serve.users` key."""
+    from aiohttp import web
+
+    captured: dict = {}
+
+    def capture_app(app, **kwargs):
+        captured["app"] = app
+
+    monkeypatch.setattr(web, "run_app", capture_app)
+    from unshackle.core.config import config as cfg
+
+    monkeypatch.setattr(
+        cfg,
+        "serve",
+        {"api_secret": "master-key", "users": {"user-key": {"username": "alice", "services": ["EXAMPLE"]}}},
+    )
+
+    result = runner.invoke(serve, ["--api-only", "--remote-only"])
+    assert result.exit_code == 0, result.output
+
+    app = captured["app"]
+    assert set(app["config"]["users"]) == {"master-key", "user-key"}
+    assert app["config"]["users"]["user-key"]["username"] == "alice"
+
+    client = await aiohttp_client(app)
+    # an unrouted path still passes through the auth middleware first
+    assert (await client.get("/api/unknown", headers={"X-Secret-Key": "user-key"})).status == 404
+    assert (await client.get("/api/unknown", headers={"X-Secret-Key": "master-key"})).status == 404
+    assert (await client.get("/api/unknown", headers={"X-Secret-Key": "nope"})).status == 401
+
+
+async def test_api_only_coerces_non_str_user_keys(
+    runner: CliRunner, monkeypatch: pytest.MonkeyPatch, aiohttp_client
+) -> None:
+    """A yaml users key that parses as int must still authenticate (compare_digest needs str)."""
+    from aiohttp import web
+
+    captured: dict = {}
+    monkeypatch.setattr(web, "run_app", lambda app, **kwargs: captured.update(app=app))
+    from unshackle.core.config import config as cfg
+
+    monkeypatch.setattr(cfg, "serve", {"api_secret": "master-key", "users": {123456: {"username": "bob"}}})
+
+    result = runner.invoke(serve, ["--api-only", "--remote-only"])
+    assert result.exit_code == 0, result.output
+    assert "123456" in captured["app"]["config"]["users"]
+
+    client = await aiohttp_client(captured["app"])
+    assert (await client.get("/api/unknown", headers={"X-Secret-Key": "123456"})).status == 404
+    assert (await client.get("/api/unknown", headers={"X-Secret-Key": "master-key"})).status == 404
+
+
 def test_serve_without_no_key_requires_api_secret(runner: CliRunner, monkeypatch: pytest.MonkeyPatch) -> None:
     from unshackle.core.config import config as cfg
 
diff --git a/unshackle/commands/serve.py b/unshackle/commands/serve.py
index f46dc9a1..3480f9de 100644
--- a/unshackle/commands/serve.py
+++ b/unshackle/commands/serve.py
@@ -160,6 +160,10 @@ def serve(
         if global_services:
             log.info(f"Global service allowlist: {', '.join(global_services)}")
         users = config.serve.get("users", {})
+        if isinstance(users, dict):
+            # yaml keys can parse as int; hmac.compare_digest and allowlist lookups need str
+            users = {str(k): v for k, v in users.items()}
+            config.serve["users"] = users
         for user_key, user_cfg in users.items() if isinstance(users, dict) else []:
             user_services = user_cfg.get("services") if isinstance(user_cfg, dict) else None
             if user_services:
@@ -173,7 +177,10 @@ def serve(
                 app["config"] = {"users": {}}
             else:
                 app = web.Application(middlewares=[cors_middleware, api_key_authentication, compression_middleware])
-                app["config"] = {"users": {api_secret: {"devices": [], "username": "api_user"}}}
+                api_users: dict = {api_secret: {"devices": [], "username": "api_user"}}
+                if isinstance(users, dict):
+                    api_users.update(users)
+                app["config"] = {"users": api_users}
             app["debug_api"] = debug_api
 
             # Start session cleanup loop for remote-dl sessions
diff --git a/unshackle/core/remote_service.py b/unshackle/core/remote_service.py
index 214a30df..53ab60c1 100644
--- a/unshackle/core/remote_service.py
+++ b/unshackle/core/remote_service.py
@@ -37,6 +37,8 @@ log = logging.getLogger("remote_service")
 
 SENSITIVE_DATA_KEYS = ("credential", "credentials", "password", "token", "api_key")
 
+DEFAULT_AUTH_HEADERS = ["X-Secret-Key", "X-Api-Key"]
+
 
 def redact_secrets(text: str, data: Optional[Dict[str, Any]] = None) -> str:
     """Mask URL userinfo and any request-payload secrets before the text is logged."""
@@ -47,9 +49,11 @@ def redact_secrets(text: str, data: Optional[Dict[str, Any]] = None) -> str:
 class RemoteClient:
     """HTTP client for the unshackle serve API."""
 
-    def __init__(self, server_url: str, api_key: str) -> None:
+    def __init__(self, server_url: str, api_key: str, auth_headers: Optional[list[str]] = None) -> None:
         self.server_url = server_url.rstrip("/")
         self.api_key = api_key
+        self.auth_headers = list(auth_headers) if auth_headers else list(DEFAULT_AUTH_HEADERS)
+        self._auth_header_index = 0
         self._session: Optional[requests.Session] = None
 
     @property
@@ -60,20 +64,35 @@ class RemoteClient:
             self._session = requests.Session()
             self._session.headers["User-Agent"] = f"unshackle/{__version__}"
             if self.api_key:
-                self._session.headers["X-Secret-Key"] = self.api_key
+                self._session.headers[self.auth_headers[self._auth_header_index]] = self.api_key
         return self._session
 
+    def _next_auth_header(self) -> bool:
+        """Move the api key onto the next candidate header. False once they are exhausted."""
+        if not self.api_key or self._auth_header_index + 1 >= len(self.auth_headers):
+            return False
+        session = self.session
+        session.headers.pop(self.auth_headers[self._auth_header_index], None)
+        self._auth_header_index += 1
+        session.headers[self.auth_headers[self._auth_header_index]] = self.api_key
+        return True
+
     def _request(self, method: str, endpoint: str, data: Optional[Dict[str, Any]] = None) -> Dict[str, Any]:
         url = f"{self.server_url}{endpoint}"
-        try:
-            resp = getattr(self.session, method)(url, json=data, timeout=120 if method == "post" else 30)
-        except requests.ConnectionError:
-            server_url = safe_display_url(self.server_url)
-            log.error(f"Could not connect to remote server at {server_url}. Is it running? (unshackle serve)")
-            raise SystemExit(1)
-        except requests.Timeout:
-            log.error(f"Request to remote server timed out: {endpoint}")
-            raise SystemExit(1)
+        while True:
+            try:
+                resp = getattr(self.session, method)(url, json=data, timeout=120 if method == "post" else 30)
+            except requests.ConnectionError:
+                server_url = safe_display_url(self.server_url)
+                log.error(f"Could not connect to remote server at {server_url}. Is it running? (unshackle serve)")
+                raise SystemExit(1)
+            except requests.Timeout:
+                log.error(f"Request to remote server timed out: {endpoint}")
+                raise SystemExit(1)
+            # servers differ on which header carries the key, so retry the rest before giving up
+            if resp.status_code == 401 and self._next_auth_header():
+                continue
+            break
         result = resp.json()
         if resp.status_code >= 400:
             error_msg = redact_secrets(str(result.get("message", resp.text)), data)
@@ -319,8 +338,31 @@ def _build_title(info: Dict[str, Any], service_tag: str, fallback_id: str) -> Un
     return title
 
 
+def _resolve_auth_headers(svc: dict, server_name: str) -> list[str]:
+    """Configured header names first, then the defaults as fallbacks."""
+    auth_headers = svc.get("auth_headers")
+    if auth_headers is None:
+        return list(DEFAULT_AUTH_HEADERS)
+    if (
+        not isinstance(auth_headers, list)
+        or not auth_headers
+        or not all(isinstance(h, str) and h.strip() for h in auth_headers)
+    ):
+        raise click.ClickException(
+            f"Remote service '{server_name}': 'auth_headers' must be a list of header names, e.g.\n\n"
+            '      auth_headers: ["Authorization"]'
+        )
+    resolved = [h.strip() for h in auth_headers]
+    seen = {h.lower() for h in resolved}
+    resolved.extend(h for h in DEFAULT_AUTH_HEADERS if h.lower() not in seen)
+    return resolved
+
+
 def resolve_server(server_name: Optional[str]) -> tuple[str, str, dict]:
-    """Resolve server URL, API key, and per-service config from remote_services."""
+    """Resolve server URL, API key, and per-service config from remote_services.
+
+    The per-service config carries the ``_auth_headers`` candidate list for RemoteClient.
+    """
     remote_services = config.remote_services
     if not remote_services:
         raise click.ClickException(
@@ -338,6 +380,7 @@ def resolve_server(server_name: Optional[str]) -> tuple[str, str, dict]:
             raise click.ClickException(f"Remote service '{server_name}' not found. Available: {available}")
         services = svc.get("services", {})
         services["_server_cdm"] = svc.get("server_cdm", False)
+        services["_auth_headers"] = _resolve_auth_headers(svc, server_name)
         return svc["url"], svc.get("api_key", ""), services
 
     if len(remote_services) == 1:
@@ -345,6 +388,7 @@ def resolve_server(server_name: Optional[str]) -> tuple[str, str, dict]:
         log.info(f"Using remote service: {name}")
         services = svc.get("services", {})
         services["_server_cdm"] = svc.get("server_cdm", False)
+        services["_auth_headers"] = _resolve_auth_headers(svc, name)
         return svc["url"], svc.get("api_key", ""), services
 
     available = ", ".join(remote_services.keys())
@@ -415,7 +459,7 @@ class RemoteService:
 
         self.service_tag = service_tag
         self.title_id = title_id
-        self.client = RemoteClient(server_url, api_key)
+        self.client = RemoteClient(server_url, api_key, services_config.get("_auth_headers"))
         self.ctx = ctx
         self._service_params = service_params or {}
         self.log = logging.getLogger(service_tag)
diff --git a/unshackle/core/services.py b/unshackle/core/services.py
index aa3ca24d..88fa50f9 100644
--- a/unshackle/core/services.py
+++ b/unshackle/core/services.py
@@ -204,8 +204,8 @@ class Services(click.Group):
             from unshackle.core.remote_service import RemoteClient, resolve_server
 
             server_name = ctx.params.get("server")
-            server_url, api_key, _ = resolve_server(server_name)
-            client = RemoteClient(server_url, api_key)
+            server_url, api_key, services_config = resolve_server(server_name)
+            client = RemoteClient(server_url, api_key, services_config.get("_auth_headers"))
             result = client.get("/api/services")
             Services._remote_services_cache = result.get("services", [])
             return Services._remote_services_cache