Extend web_client_location to handle absolute URLs

changelog.d/7006.feature

@@ -0,0 +1 @@
+Extend the `web_client_location` option to accept an absolute URL to use as a redirect. Adds a warning when running the web client on the same hostname as homeserver. Contributed by Martin Milata.

docs/sample_config.yaml

@@ -33,10 +33,15 @@ server_name: "SERVERNAME"
 #
 pid_file: DATADIR/homeserver.pid
 
-# The path to the web client which will be served at /_matrix/client/
-# if 'webclient' is configured under the 'listeners' configuration.
+# The absolute URL to the web client which /_matrix/client will redirect
+# to if 'webclient' is configured under the 'listeners' configuration.
 #
-#web_client_location: "/path/to/web/root"
+# This option can be also set to the filesystem path to the web client
+# which will be served at /_matrix/client/ if 'webclient' is configured
+# under the 'listeners' configuration, however this is a security risk:
+# https://github.com/matrix-org/synapse#security-note
+#
+#web_client_location: https://riot.example.com/
 
 # The public-facing base URL that clients use to access this HS
 # (not including _matrix/...). This is the same URL a user would

synapse/app/homeserver.py

@@ -241,16 +241,26 @@ def _configure_named_resource(self, name, compress=False):
             resources[SERVER_KEY_V2_PREFIX] = KeyApiV2Resource(self)
 
         if name == "webclient":
-            webclient_path = self.get_config().web_client_location
+            webclient_loc = self.get_config().web_client_location
 
-            if webclient_path is None:
+            if webclient_loc is None:
                 logger.warning(
                     "Not enabling webclient resource, as web_client_location is unset."
                 )
+            elif webclient_loc.startswith("http://") or webclient_loc.startswith(
+                "https://"
+            ):
+                resources[WEB_CLIENT_PREFIX] = RootRedirect(webclient_loc)
             else:
+                logger.warning(
+                    "Running webclient on the same domain is not recommended: "
+                    "https://github.com/matrix-org/synapse#security-note - "
+                    "after you move webclient to different host you can set "
+                    "web_client_location to its full URL to enable redirection."
+                )
                 # GZip is disabled here due to
                 # https://twistedmatrix.com/trac/ticket/7678
-                resources[WEB_CLIENT_PREFIX] = File(webclient_path)
+                resources[WEB_CLIENT_PREFIX] = File(webclient_loc)
 
         if name == "metrics" and self.get_config().enable_metrics:
             resources[METRICS_PREFIX] = MetricsResource(RegistryProxy)

synapse/config/server.py

@@ -604,10 +604,15 @@ def generate_config_section(
         #
         pid_file: %(pid_file)s
 
-        # The path to the web client which will be served at /_matrix/client/
-        # if 'webclient' is configured under the 'listeners' configuration.
+        # The absolute URL to the web client which /_matrix/client will redirect
+        # to if 'webclient' is configured under the 'listeners' configuration.
         #
-        #web_client_location: "/path/to/web/root"
+        # This option can be also set to the filesystem path to the web client
+        # which will be served at /_matrix/client/ if 'webclient' is configured
+        # under the 'listeners' configuration, however this is a security risk:
+        # https://github.com/matrix-org/synapse#security-note
+        #
+        #web_client_location: https://riot.example.com/
 
         # The public-facing base URL that clients use to access this HS
         # (not including _matrix/...). This is the same URL a user would