diff --git a/muxplex/auth.py b/muxplex/auth.py
index a6d0e22..91c049c 100644
--- a/muxplex/auth.py
+++ b/muxplex/auth.py
@@ -3,6 +3,8 @@ muxplex authentication — password and signing secret file management.
 """
 
 import base64
+import hmac
+import logging
 import secrets
 from pathlib import Path
 
@@ -11,6 +13,8 @@ from starlette.middleware.base import BaseHTTPMiddleware
 from starlette.requests import Request
 from starlette.responses import JSONResponse, RedirectResponse, Response
 
+_log = logging.getLogger(__name__)
+
 
 # ---------------------------------------------------------------------------
 # Config directory
@@ -164,12 +168,14 @@ class AuthMiddleware(BaseHTTPMiddleware):
         secret: str,
         ttl_seconds: int,
         password: str = "",
+        federation_key: str = "",
     ):
         super().__init__(app)
         self.auth_mode = auth_mode
         self.secret = secret
         self.ttl_seconds = ttl_seconds
         self.password = password
+        self.federation_key = federation_key
 
     async def dispatch(self, request: Request, call_next) -> Response:
         # 1. Localhost bypass — client.host is the socket-level IP and cannot
@@ -192,6 +198,14 @@ class AuthMiddleware(BaseHTTPMiddleware):
         if cookie and verify_session_cookie(self.secret, cookie, self.ttl_seconds):
             return await call_next(request)
 
+        # 4a. Bearer token (server-to-server federation)
+        auth_header = request.headers.get("authorization", "")
+        if self.federation_key and auth_header.lower().startswith("bearer "):
+            token = auth_header[7:]
+            if hmac.compare_digest(token, self.federation_key):
+                return await call_next(request)
+            _log.warning("federation: rejected Bearer from %s", client_host)
+
         # 4b. X-Muxplex-Token header (for cross-origin federation)
         token_header = request.headers.get("x-muxplex-token")
         if token_header:
diff --git a/muxplex/tests/test_auth.py b/muxplex/tests/test_auth.py
index a000854..9e7fd52 100644
--- a/muxplex/tests/test_auth.py
+++ b/muxplex/tests/test_auth.py
@@ -484,3 +484,68 @@ def test_middleware_invalid_token_header_falls_through_to_redirect():
     response = client.get("/protected", headers={"X-Muxplex-Token": "bad.token.value"})
     # Invalid token: should NOT pass auth, falls through to redirect or 401
     assert response.status_code in (307, 401)
+
+
+# ---------------------------------------------------------------------------
+# Bearer token auth (server-to-server federation)
+# ---------------------------------------------------------------------------
+
+
+def _make_federation_app(federation_key: str = "fed-key") -> FastAPI:
+    """Create a minimal FastAPI app with AuthMiddleware configured with a federation_key."""
+    test_app = FastAPI()
+
+    test_app.add_middleware(
+        AuthMiddleware,
+        auth_mode="password",
+        secret="test-secret",
+        ttl_seconds=3600,
+        password="test-pw",
+        federation_key=federation_key,
+    )
+
+    @test_app.get("/protected")
+    async def protected():
+        return PlainTextResponse("OK")
+
+    return test_app
+
+
+def test_middleware_valid_bearer_token_passes():
+    """Non-localhost with valid Bearer token and federation_key configured passes through (200)."""
+    app = _make_federation_app(federation_key="my-federation-secret")
+    client = TestClient(app, base_url="http://192.168.1.1")
+    response = client.get(
+        "/protected", headers={"Authorization": "Bearer my-federation-secret"}
+    )
+    assert response.status_code == 200
+    assert response.text == "OK"
+
+
+def test_middleware_invalid_bearer_token_falls_through():
+    """Non-localhost with wrong Bearer token falls through to 401 (not accepted)."""
+    app = _make_federation_app(federation_key="my-federation-secret")
+    client = TestClient(app, base_url="http://192.168.1.1", follow_redirects=False)
+    response = client.get(
+        "/protected",
+        headers={
+            "Authorization": "Bearer wrong-token",
+            "Accept": "application/json",
+        },
+    )
+    assert response.status_code == 401
+
+
+def test_middleware_bearer_skipped_when_no_federation_key():
+    """Empty federation_key means Bearer tokens are never accepted (falls through to 401)."""
+    app = _make_federation_app(federation_key="")
+    client = TestClient(app, base_url="http://192.168.1.1", follow_redirects=False)
+    response = client.get(
+        "/protected",
+        headers={
+            "Authorization": "Bearer any-token-value",
+            "Accept": "application/json",
+        },
+    )
+    # Bearer should be skipped when federation_key is empty, falls through to 401
+    assert response.status_code == 401