diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 099324a8..064493e1 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -208,7 +208,8 @@ class TelegramBaseClient(abc.ABC):
             state, connection, self._loop,
             retries=self._connection_retries,
             auto_reconnect=self._auto_reconnect,
-            update_callback=self._handle_update
+            update_callback=self._handle_update,
+            auth_key_callback=self._auth_key_callback
         )
 
         # Cache :tl:`ExportedAuthorization` as ``dc_id: MTProtoState``
@@ -271,7 +272,6 @@ class TelegramBaseClient(abc.ABC):
         """
         Connects to Telegram.
         """
-        old_auth = self.session.auth_key
         await self._sender.connect(
             self.session.server_address, self.session.port)
 
@@ -280,10 +280,6 @@ class TelegramBaseClient(abc.ABC):
 
         self._updates_handle = self._loop.create_task(self._update_loop())
 
-        if old_auth != self._sender.state.auth_key:
-            self.session.auth_key = self._sender.state.auth_key
-            self.session.save()
-
     def is_connected(self):
         """
         Returns ``True`` if the user has connected.
@@ -339,6 +335,15 @@ class TelegramBaseClient(abc.ABC):
         await self._disconnect()
         return await self.connect()
 
+    def _auth_key_callback(self, auth_key):
+        """
+        Callback from the sender whenever it needed to generate a
+        new authorization key. This means we are not authorized.
+        """
+        self._authorized = None
+        self.session.auth_key = auth_key
+        self.session.save()
+
     # endregion
 
     # region Working with different connections/Data Centers
diff --git a/telethon/network/mtprotosender.py b/telethon/network/mtprotosender.py
index eb167cff..0d40e6b6 100644
--- a/telethon/network/mtprotosender.py
+++ b/telethon/network/mtprotosender.py
@@ -41,7 +41,8 @@ class MTProtoSender:
     key exists yet.
     """
     def __init__(self, state, connection, loop, *,
-                 retries=5, auto_reconnect=True, update_callback=None):
+                 retries=5, auto_reconnect=True, update_callback=None,
+                 auth_key_callback=None):
         self.state = state
         self._connection = connection
         self._loop = loop
@@ -50,6 +51,7 @@ class MTProtoSender:
         self._retries = retries
         self._auto_reconnect = auto_reconnect
         self._update_callback = update_callback
+        self._auth_key_callback = auth_key_callback
 
         # Whether the user has explicitly connected or disconnected.
         #
@@ -255,6 +257,10 @@ class MTProtoSender:
                     __log__.debug('New auth_key attempt {}...'.format(retry))
                     self.state.auth_key, self.state.time_offset =\
                         await authenticator.do_authentication(plain)
+
+                    if self._auth_key_callback:
+                        self._auth_key_callback(self.state.auth_key)
+
                     break
                 except (SecurityError, AssertionError) as e:
                     __log__.warning('Attempt {} at new auth_key failed: {}'