Add httpx.SSLContext configuration.

httpx/_client.py

@@ -1455,6 +1455,9 @@ def _init_proxy_transport(
     ) -> AsyncBaseTransport:
         return AsyncHTTPTransport(
             ssl_context=ssl_context,
+            verify=verify,
+            cert=cert,
+            http1=http1,
             http2=http2,
             limits=limits,
             proxy=proxy,