Normalize request paths in media auth (#24662)

* merge repeated slashes in the media auth path check

X-Original-URL carries only the raw request path since #24602, and extract_path parsed it with urlparse, which reads a path starting with // as a host. A restricted role could request another camera's clips or recordings with a leading // and the media check saw a non-media path and allowed it, while nginx merged the slashes and served the file. extract_path now splits the raw URI the same way the go2rtc stream check does and merges repeated slashes as nginx does before matching locations. The split helper moves from auth.py into media_auth.py so both checks share it.

* check the nginx-normalized path in the media auth dot-segment fallback

The dot-segment fallback only checked the raw first segment, so a role restricted to one camera could request `/x/../clips/back_door-1.jpg` and nginx served back_door's clip. The fallback now resolves the path the way nginx does before checking for a media root, and the URI split ends at a literal `#` since nginx ignores everything after it.

frigate/test/test_media_auth.py

@@ -76,6 +76,20 @@ class TestExtractPath(unittest.TestCase):
         self.assertIsNone(extract_path(None))
         self.assertIsNone(extract_path(""))
 
+    def test_leading_double_slash_is_path(self):
+        self.assertEqual(
+            extract_path("//clips/front_door-1.jpg"), "/clips/front_door-1.jpg"
+        )
+
+    def test_repeated_slashes_merged(self):
+        self.assertEqual(
+            extract_path("/recordings//2026-05-11/14//front_door/00.00.mp4"),
+            "/recordings/2026-05-11/14/front_door/00.00.mp4",
+        )
+        self.assertEqual(
+            extract_path("/%2Fclips/front_door-1.jpg"), "/clips/front_door-1.jpg"
+        )
+
 
 class TestResolveMediaUri(unittest.TestCase):
     def setUp(self):
@@ -376,6 +390,34 @@ class TestDenyResponseForMediaUri(unittest.TestCase):
         self.assertIsNone(self._deny("/clips/nonexistent-1.jpg", "admin"))
         self.assertIsNone(self._deny("/clips/nonexistent-1.jpg", "viewer"))
 
+    def test_repeated_slashes_resolve_to_owning_camera(self):
+        # nginx merges repeated slashes before matching the media locations
+        for url in (
+            "//clips/back_door-1.jpg",
+            "/clips//back_door-1.jpg",
+            "//recordings/2026-05-11/14/back_door/00.00.mp4",
+            "/recordings//2026-05-11/14/back_door/00.00.mp4",
+        ):
+            self.assertEqual(self._deny(url, "limited_user"), 403, url)
+        self.assertIsNone(self._deny("//clips/front_door-1.jpg", "limited_user"))
+
+    def test_traversal_with_leading_double_slash_denied(self):
+        self.assertEqual(
+            self._deny("//clips/front_door/../back_door-1.jpg", "admin"), 403
+        )
+
+    def test_traversal_from_non_media_prefix_denied(self):
+        # nginx resolves these into a media root before serving
+        for url in (
+            "/x/../clips/back_door-1.jpg",
+            "/x/%2E%2E/clips/back_door-1.jpg",
+            "/./clips/front_door/../back_door-1.jpg",
+            "/api/../recordings/2026-05-11/14/back_door/00.00.mp4",
+            "/clips/back_door-1.jpg#/../../x",
+        ):
+            self.assertEqual(self._deny(url, "limited_user"), 403, url)
+        self.assertIsNone(self._deny("/x/../api/events", "limited_user"))
+
 
 if __name__ == "__main__":
     unittest.main()