diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 8a21b70c..e9f562bf 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -1,11 +1,10 @@
 import abc
 import asyncio
-import inspect
 import logging
 import platform
 import sys
 import time
-from datetime import timedelta, datetime
+from datetime import datetime
 
 from .. import version
 from ..crypto import rsa
@@ -14,7 +13,7 @@ from ..network import MTProtoSender, ConnectionTcpFull
 from ..sessions import Session, SQLiteSession, MemorySession
 from ..tl import TLObject, functions, types
 from ..tl.alltlobjects import LAYER
-from ..utils import AsyncClassWrapper
+from ..crypto import AuthKey
 
 DEFAULT_DC_ID = 4
 DEFAULT_IPV4_IP = '149.154.167.51'
@@ -236,12 +235,11 @@ class TelegramBaseClient(abc.ABC):
 
         self._connection = connection
         self._sender = MTProtoSender(
-            self._loop,
+            self.session.auth_key, self._loop,
             retries=self._connection_retries,
             auto_reconnect=self._auto_reconnect,
             connect_timeout=self._timeout,
             update_callback=self._handle_update,
-            auth_key_callback=self._auth_key_callback,
             auto_reconnect_callback=self._handle_auto_reconnect
         )
 
@@ -310,7 +308,7 @@ class TelegramBaseClient(abc.ABC):
         """
         Connects to Telegram.
         """
-        await self._sender.connect(self.session.auth_key, self._connection(
+        await self._sender.connect(self._connection(
             self.session.server_address, self.session.port,
             loop=self._loop, proxy=self._proxy
         ))
@@ -318,6 +316,12 @@ class TelegramBaseClient(abc.ABC):
         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):
@@ -426,8 +430,8 @@ class TelegramBaseClient(abc.ABC):
         #
         # If one were to do that, Telegram would reset the connection
         # with no further clues.
-        sender = MTProtoSender(self._loop)
-        await sender.connect(None, self._connection(
+        sender = MTProtoSender(None, self._loop)
+        await sender.connect(self._connection(
             dc.ip_address, dc.port, loop=self._loop, proxy=self._proxy))
         __log__.info('Exporting authorization for data center %s', dc)
         auth = await self(functions.auth.ExportAuthorizationRequest(dc_id))
diff --git a/telethon/network/mtprotosender.py b/telethon/network/mtprotosender.py
index ada7784d..8c853bf0 100644
--- a/telethon/network/mtprotosender.py
+++ b/telethon/network/mtprotosender.py
@@ -41,17 +41,15 @@ class MTProtoSender:
     A new authorization key will be generated on connection if no other
     key exists yet.
     """
-    def __init__(self, loop, *,
+    def __init__(self, auth_key, loop, *,
                  retries=5, auto_reconnect=True, connect_timeout=None,
-                 update_callback=None, auth_key=None,
-                 auth_key_callback=None, auto_reconnect_callback=None):
+                 update_callback=None, auto_reconnect_callback=None):
         self._connection = None
         self._loop = loop
         self._retries = retries
         self._auto_reconnect = auto_reconnect
         self._connect_timeout = connect_timeout
         self._update_callback = update_callback
-        self._auth_key_callback = auth_key_callback
         self._auto_reconnect_callback = auto_reconnect_callback
 
         # Whether the user has explicitly connected or disconnected.
@@ -107,7 +105,7 @@ class MTProtoSender:
 
     # Public API
 
-    async def connect(self, auth_key, connection):
+    async def connect(self, connection):
         """
         Connects to the specified given connection using the given auth key.
         """
@@ -115,7 +113,6 @@ class MTProtoSender:
             __log__.info('User is already connected!')
             return
 
-        self._auth_key.key = auth_key
         self._connection = connection
         self._user_connected = True
         await self._connect()
@@ -216,9 +213,6 @@ class MTProtoSender:
                     self._auth_key.key, self._state.time_offset =\
                         await authenticator.do_authentication(plain)
 
-                    if self._auth_key_callback:
-                        await self._auth_key_callback(self._auth_key)
-
                     break
                 except (SecurityError, AssertionError) as e:
                     __log__.warning('Attempt {} at new auth_key failed: {}'