diff --git a/README.rst b/README.rst
index 2ac6347..3fb2f55 100644
--- a/README.rst
+++ b/README.rst
@@ -66,6 +66,12 @@ Flask-Digest-Auth supports log out.  The user will be prompted for
 new username and password.
 
 
+Log In Bookkeeping
+##################
+
+You can register a callback to run when the user logs in.
+
+
 .. _HTTP Digest Authentication: https://en.wikipedia.org/wiki/Digest_access_authentication
 .. _RFC 2617: https://www.rfc-editor.org/rfc/rfc2617
 .. _Flask: https://flask.palletsprojects.com
@@ -336,6 +342,19 @@ the next browser automatic authentication to fail, forcing the browser
 to ask the user for the username and password again.
 
 
+Log In Bookkeeping
+=================#
+
+You can register a callback to run when the user logs in, for ex.,
+logging the log in event, adding the log in counter, etc.
+
+::
+
+    @auth.register_on_login
+    def on_login(user: User) -> None:
+        user.visits = user.visits + 1
+
+
 Writing Tests
 =============
 
diff --git a/src/flask_digest_auth/auth.py b/src/flask_digest_auth/auth.py
index 167d8df..a0b4c0e 100644
--- a/src/flask_digest_auth/auth.py
+++ b/src/flask_digest_auth/auth.py
@@ -67,6 +67,18 @@ class BaseUserGetter:
                                 " was not registered yet.")
 
 
+class BaseOnLogInCallback:
+    """The base callback when the user logs in."""
+
+    @staticmethod
+    def __call__(user: t.Any) -> None:
+        """Runs the callback when the user logs in.
+
+        :param user: The logged-in user.
+        :return: None.
+        """
+
+
 class DigestAuth:
     """The HTTP digest authentication."""
 
@@ -87,6 +99,7 @@ class DigestAuth:
         self.__get_password_hash: BasePasswordHashGetter \
             = BasePasswordHashGetter()
         self.__get_user: BaseUserGetter = BaseUserGetter()
+        self.__on_login: BaseOnLogInCallback = BaseOnLogInCallback()
 
     def login_required(self, view) -> t.Callable:
         """The view decorator for HTTP digest authentication.
@@ -125,7 +138,9 @@ class DigestAuth:
                             "Not an HTTP digest authorization")
                     self.authenticate(state)
                     session["user"] = authorization.username
-                    g.user = self.__get_user(authorization.username)
+                    user = self.__get_user(authorization.username)
+                    g.user = user
+                    self.__on_login(user)
                     return view(*args, **kwargs)
                 except UnauthorizedException as e:
                     if len(e.args) > 0:
@@ -257,6 +272,27 @@ class DigestAuth:
 
         self.__get_user = UserGetter()
 
+    def register_on_login(self, func: t.Callable[[t.Any], None]) -> None:
+        """Registers the callback when the user logs in.
+
+        :param func: The callback given the logged-in user.
+        :return: None.
+        """
+
+        class OnLogInCallback:
+            """The callback when the user logs in."""
+
+            @staticmethod
+            def __call__(user: t.Any) -> None:
+                """Runs the callback when the user logs in.
+
+                :param user: The logged-in user.
+                :return: None.
+                """
+                func(user)
+
+        self.__on_login = OnLogInCallback()
+
     def init_app(self, app: Flask) -> None:
         """Initializes the Flask application.
 
@@ -303,6 +339,7 @@ class DigestAuth:
                     user = login_manager.user_callback(
                         authorization.username)
                     login_user(user)
+                    self.__on_login(user)
                     return user
                 except UnauthorizedException as e:
                     if str(e) != "":
diff --git a/tests/test_auth.py b/tests/test_auth.py
index fcb6751..241a211 100644
--- a/tests/test_auth.py
+++ b/tests/test_auth.py
@@ -20,7 +20,6 @@
 """
 import typing as t
 from secrets import token_urlsafe
-from types import SimpleNamespace
 
 from flask import Response, Flask, g, redirect, request
 from flask_testing import TestCase
@@ -33,6 +32,20 @@ _USERNAME: str = "Mufasa"
 _PASSWORD: str = "Circle Of Life"
 
 
+class User:
+    """A dummy user"""
+
+    def __init__(self, username: str, password_hash: str):
+        """Constructs a dummy user.
+
+        :param username: The username.
+        :param password_hash: The password hash.
+        """
+        self.username: str = username
+        self.password_hash: str = password_hash
+        self.visits: int = 0
+
+
 class AuthenticationTestCase(TestCase):
     """The test case for the HTTP digest authentication."""
 
@@ -50,8 +63,9 @@ class AuthenticationTestCase(TestCase):
 
         auth: DigestAuth = DigestAuth(realm=_REALM)
         auth.init_app(app)
-        user_db: t.Dict[str, str] \
-            = {_USERNAME: make_password_hash(_REALM, _USERNAME, _PASSWORD)}
+        user_db: t.Dict[str, User] \
+            = {_USERNAME: User(
+                   _USERNAME, make_password_hash(_REALM, _USERNAME, _PASSWORD))}
 
         @auth.register_get_password
         def get_password_hash(username: str) -> t.Optional[str]:
@@ -60,7 +74,8 @@ class AuthenticationTestCase(TestCase):
             :param username: The username.
             :return: The password hash, or None if the user does not exist.
             """
-            return user_db[username] if username in user_db else None
+            return user_db[username].password_hash if username in user_db \
+                else None
 
         @auth.register_get_user
         def get_user(username: str) -> t.Optional[t.Any]:
@@ -69,8 +84,16 @@ class AuthenticationTestCase(TestCase):
             :param username: The username.
             :return: The user, or None if the user does not exist.
             """
-            return SimpleNamespace(username=username) if username in user_db \
-                else None
+            return user_db[username] if username in user_db else None
+
+        @auth.register_on_login
+        def on_login(user: User):
+            """The callback when the user logs in.
+
+            :param user: The logged-in user.
+            :return: None.
+            """
+            user.visits = user.visits + 1
 
         @app.get("/admin-1/auth", endpoint="admin-1")
         @auth.login_required
@@ -118,6 +141,7 @@ class AuthenticationTestCase(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.data.decode("UTF-8"),
                          f"Hello, {_USERNAME}! #2")
+        self.assertEqual(g.user.visits, 1)
 
     def test_stale_opaque(self) -> None:
         """Tests the stale and opaque value.
@@ -194,3 +218,4 @@ class AuthenticationTestCase(TestCase):
 
         response = self.client.get(admin_uri)
         self.assertEqual(response.status_code, 200)
+        self.assertEqual(g.user.visits, 2)
diff --git a/tests/test_flask_login.py b/tests/test_flask_login.py
index f1348f5..679c3af 100644
--- a/tests/test_flask_login.py
+++ b/tests/test_flask_login.py
@@ -21,6 +21,7 @@
 import typing as t
 from secrets import token_urlsafe
 
+import flask_login
 from flask import Response, Flask, g, redirect, request
 from flask_testing import TestCase
 from werkzeug.datastructures import WWWAuthenticate, Authorization
@@ -35,12 +36,15 @@ _PASSWORD: str = "Circle Of Life"
 class User:
     """A dummy user."""
 
-    def __init__(self, username: str):
+    def __init__(self, username: str, password_hash: str):
         """Constructs a dummy user.
 
         :param username: The username.
+        :param password_hash: The password hash.
         """
         self.username: str = username
+        self.password_hash: str = password_hash
+        self.visits: int = 0
         self.is_authenticated: bool = True
         self.is_active: bool = True
         self.is_anonymous: bool = False
@@ -82,8 +86,9 @@ class FlaskLoginTestCase(TestCase):
         auth: DigestAuth = DigestAuth(realm=_REALM)
         auth.init_app(app)
 
-        user_db: t.Dict[str, str] \
-            = {_USERNAME: make_password_hash(_REALM, _USERNAME, _PASSWORD)}
+        user_db: t.Dict[str, User] \
+            = {_USERNAME: User(
+                   _USERNAME, make_password_hash(_REALM, _USERNAME, _PASSWORD))}
 
         @auth.register_get_password
         def get_password_hash(username: str) -> t.Optional[str]:
@@ -92,7 +97,17 @@ class FlaskLoginTestCase(TestCase):
             :param username: The username.
             :return: The password hash, or None if the user does not exist.
             """
-            return user_db[username] if username in user_db else None
+            return user_db[username].password_hash if username in user_db \
+                else None
+
+        @auth.register_on_login
+        def on_login(user: User):
+            """The callback when the user logs in.
+
+            :param user: The logged-in user.
+            :return: None.
+            """
+            user.visits = user.visits + 1
 
         @login_manager.user_loader
         def load_user(user_id: str) -> t.Optional[User]:
@@ -101,7 +116,7 @@ class FlaskLoginTestCase(TestCase):
             :param user_id: The username.
             :return: The user, or None if the user does not exist.
             """
-            return User(user_id) if user_id in user_db else None
+            return user_db[user_id] if user_id in user_db else None
 
         @app.get("/admin-1/auth", endpoint="admin-1")
         @flask_login.login_required
@@ -152,6 +167,7 @@ class FlaskLoginTestCase(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.data.decode("UTF-8"),
                          f"Hello, {_USERNAME}! #2")
+        self.assertEqual(flask_login.current_user.visits, 1)
 
     def test_stale_opaque(self) -> None:
         """Tests the stale and opaque value.
@@ -237,3 +253,4 @@ class FlaskLoginTestCase(TestCase):
 
         response = self.client.get(admin_uri)
         self.assertEqual(response.status_code, 200)
+        self.assertEqual(flask_login.current_user.visits, 2)