Support Python's ConnectionRefusedError to reject a connection

docs/server.rst

@@ -246,6 +246,8 @@ a :class:`socketio.exceptions.ConnectionRefusedError` exception can be raised,
 and all of its arguments will be sent to the client with the rejection
 message::
 
+    from socketio.exceptions import ConnectionRefusedError
+
     @sio.event
     def connect(sid, environ, auth):
         raise ConnectionRefusedError('authentication failed')

src/socketio/async_server.py

@@ -561,6 +561,9 @@ class AsyncServer(base_server.BaseServer):
         except exceptions.ConnectionRefusedError as exc:
             fail_reason = exc.error_args
             success = False
+        except ConnectionRefusedError as exc:
+            fail_reason = {"message": "Connection refused by server"}
+            success = False
 
         if success is False:
             if self.always_connect:

src/socketio/server.py

@@ -543,6 +543,9 @@ class Server(base_server.BaseServer):
         except exceptions.ConnectionRefusedError as exc:
             fail_reason = exc.error_args
             success = False
+        except ConnectionRefusedError as exc:
+            fail_reason = {"message": "Connection refused by server"}
+            success = False
 
         if success is False:
             if self.always_connect: