Support for routing outbound HTTP requests via a proxy (#6239)

The `http_proxy` and `HTTPS_PROXY` env vars can be set to a `host[:port]` value which should point to a proxy.

The address of the proxy should be excluded from IP blacklists such as the `url_preview_ip_range_blacklist`.

The proxy will then be used for
 * push
 * url previews
 * phone-home stats
 * recaptcha validation
 * CAS auth validation

It will *not* be used for:
 * Application Services
 * Identity servers
 * Outbound federation
 * In worker configurations, connections from workers to masters

Fixes #4198.

2 files changed, 3 insertions, 1 deletions

diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py

index 3b60728628..7c86b88f30 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -403,7 +403,7 @@ class CasTicketServlet(RestServlet):
         self.cas_service_url = hs.config.cas_service_url
         self.cas_required_attributes = hs.config.cas_required_attributes
         self._sso_auth_handler = SSOAuthHandler(hs)
-        self._http_client = hs.get_simple_http_client()
+        self._http_client = hs.get_proxied_http_client()
 
     @defer.inlineCallbacks
     def on_GET(self, request):
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py

index acf87709f2..85a7c61a24 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -75,6 +75,8 @@ class PreviewUrlResource(Resource):
             treq_args={"browser_like_redirects": True},
             ip_whitelist=hs.config.url_preview_ip_range_whitelist,
             ip_blacklist=hs.config.url_preview_ip_range_blacklist,
+            http_proxy=os.getenv("http_proxy"),
+            https_proxy=os.getenv("HTTPS_PROXY"),
         )
         self.media_repo = media_repo
         self.primary_base_path = media_repo.primary_base_path