diff --git a/bot_bottle/egress.py b/bot_bottle/egress.py
index 663996e..22b3dfc 100644
--- a/bot_bottle/egress.py
+++ b/bot_bottle/egress.py
@@ -255,6 +255,8 @@ def _route_to_yaml_fields(r: Route) -> dict[str, object]:
         fields["matches"] = matches_data
     if r.git_fetch:
         fields["git"] = {"fetch": True}
+    if r.preserve_auth:
+        fields["preserve_auth"] = True
     if (
         r.outbound_detectors is not None
         or r.inbound_detectors is not None
@@ -335,6 +337,8 @@ def egress_render_routes(
             lines.append("    git:")
             if git_dict.get("fetch") is True:
                 lines.append("      fetch: true")
+        if f.get("preserve_auth") is True:
+            lines.append("    preserve_auth: true")
         if "dlp" in f:
             dlp_dict: dict[str, object] = f["dlp"]  # type: ignore
             lines.append("    dlp:")
diff --git a/tests/unit/test_egress.py b/tests/unit/test_egress.py
index 2db81b7..43cb73d 100644
--- a/tests/unit/test_egress.py
+++ b/tests/unit/test_egress.py
@@ -379,6 +379,25 @@ class TestRenderRoutes(unittest.TestCase):
         addon_routes = load_config(rendered).routes
         self.assertTrue(addon_routes[0].git_fetch)
 
+    def test_preserve_auth_round_trips_to_the_addon(self):
+        """Regression: the manifest parsed preserve_auth and the addon honored
+        it, but the renderer in between dropped it — so the flag never reached
+        the proxy and registry pulls kept failing with "unauthorized" while
+        the config looked correct everywhere it was inspected."""
+        from bot_bottle.egress_addon_core import load_config
+        b = _bottle([{"host": "registry-1.docker.io", "preserve_auth": True}])
+        routes = egress_routes_for_bottle(b)
+        rendered = egress_render_routes(routes)
+        self.assertIn("preserve_auth: true", rendered)
+        self.assertTrue(load_config(rendered).routes[0].preserve_auth)
+
+    def test_preserve_auth_omitted_when_unset(self):
+        b = _bottle([{"host": "x.example"}])
+        rendered = egress_render_routes(egress_routes_for_bottle(b))
+        self.assertNotIn("preserve_auth", rendered)
+        from bot_bottle.egress_addon_core import load_config
+        self.assertFalse(load_config(rendered).routes[0].preserve_auth)
+
     def test_log_zero_omitted_from_render(self):
         b = _bottle([{"host": "x.example"}])
         routes = egress_routes_for_bottle(b)