diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 9696d60c..2846bed6 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -312,16 +312,11 @@ class TelegramBaseClient(abc.ABC):
             self.session.server_address, self.session.port,
             loop=self._loop, proxy=self._proxy
         ))
+        self.session.auth_key = self._sender.auth_key
 
         await self._sender.send(self._init_with(
             functions.help.GetConfigRequest()))
 
-        # AuthKey is a property, so re-setting it has side-effects.
-        # Since it's used as a reference and only its inner payload
-        # may have actually changed after connecting, we use the
-        # reference from the session file itself as its value.
-        self.session.auth_key = self.session.auth_key
-
         self._updates_handle = self._loop.create_task(self._update_loop())
 
     def is_connected(self):
diff --git a/telethon/network/mtprotosender.py b/telethon/network/mtprotosender.py
index b4347586..28a2da8e 100644
--- a/telethon/network/mtprotosender.py
+++ b/telethon/network/mtprotosender.py
@@ -68,8 +68,8 @@ class MTProtoSender:
         self._recv_loop_handle = None
 
         # Preserving the references of the AuthKey and state is important
-        self._auth_key = auth_key or AuthKey(None)
-        self._state = MTProtoState(self._auth_key)
+        self.auth_key = auth_key or AuthKey(None)
+        self._state = MTProtoState(self.auth_key)
 
         # Outgoing messages are put in a queue and sent in a batch.
         # Note that here we're also storing their ``_RequestState``.
@@ -204,12 +204,12 @@ class MTProtoSender:
                                   .format(self._retries))
 
         __log__.debug('Connection success!')
-        if not self._auth_key:
+        if not self.auth_key:
             plain = MTProtoPlainSender(self._connection)
             for retry in range(1, self._retries + 1):
                 try:
                     __log__.debug('New auth_key attempt {}...'.format(retry))
-                    self._auth_key.key, self._state.time_offset =\
+                    self.auth_key.key, self._state.time_offset =\
                         await authenticator.do_authentication(plain)
 
                     break
@@ -402,7 +402,7 @@ class MTProtoSender:
                 else:
                     __log__.warning('Invalid buffer %s', e)
 
-                self._auth_key.key = None
+                self.auth_key.key = None
                 self._start_reconnect()
                 return
             except Exception: