Advanced to version 0.2.1.

.gitignore

@@ -23,10 +23,13 @@ dist
 .pytest_cache
 venv
 
-flask_session
-instance
-
 .DS_Store
 .idea
 
+instance
+flask_session
+
+.scannerwork
+sonar-project.properties
+
 excludes

README.rst

@@ -12,6 +12,10 @@ views.
 
 HTTP Digest Authentication is specified in `RFC 2617`_.
 
+
+Why HTTP Digest Authentication?
+-------------------------------
+
 HTTP Digest Authentication has the advantage that it does not send the
 actual password to the server, which greatly enhances the security.
 It uses the challenge-response authentication scheme.  The client
@@ -28,6 +32,46 @@ Flask-Digest-Auth works with Flask-Login_.  Log in protection can be
 separated with the authentication mechanism.  You can create protected
 Flask modules without knowing the actual authentication mechanisms.
 
+
+Features
+--------
+
+There are a couple of Flask HTTP digest authentication
+implementations.  Flask-Digest-Auth has the following features:
+
+
+Flask-Login Integration
+#######################
+
+Flask-Digest-Auth features Flask-Login integration.  The views
+can be totally independent with the actual authentication mechanism.
+You can write a Flask module that requires log in, without specify
+the actual authentication mechanism.  The application can specify
+either HTTP Digest Authentication, or the log in forms, as needed.
+
+
+Session Integration
+###################
+
+Flask-Digest-Auth features session integration.  The user log in
+is remembered in the session.  The authentication information is not
+requested again.  This is different to the practice of the HTTP Digest
+Authentication, but is convenient for the log in accounting.
+
+
+Log Out Support
+###############
+
+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
@@ -60,6 +104,8 @@ Flask-Digest-Auth Alone
 
 Flask-Digest-Auth can authenticate the users alone.
 
+The currently logged-in user can be retrieved at ``g.user``, if any.
+
 
 Example for Simple Applications with Flask-Digest-Auth Alone
 ------------------------------------------------------------
@@ -75,6 +121,7 @@ In your ``my_app.py``:
     ... (Configure the Flask application) ...
 
     auth: DigestAuth = DigestAuth(realm="Admin")
+    auth.init_app(app)
 
     @auth.register_get_password
     def get_password_hash(username: str) -> t.Optional[str]:
@@ -87,7 +134,7 @@ In your ``my_app.py``:
     @app.get("/admin")
     @auth.login_required
     def admin():
-        ... (Process the view) ...
+        return f"Hello, {g.user.username}!"
 
     @app.post("/logout")
     @auth.login_required
@@ -113,6 +160,7 @@ In your ``my_app/__init__.py``:
         ... (Configure the Flask application) ...
 
         auth.realm = app.config["REALM"]
+        auth.init_app(app)
 
         @auth.register_get_password
         def get_password_hash(username: str) -> t.Optional[str]:
@@ -136,7 +184,7 @@ In your ``my_app/views.py``:
     @bp.get("/admin")
     @auth.login_required
     def admin():
-        ... (Process the view) ...
+        return f"Hello, {g.user.username}!"
 
     @app.post("/logout")
     @auth.login_required
@@ -156,6 +204,12 @@ module that requires log in, without specifying the authentication
 mechanism.  The Flask application can specify the actual
 authentication mechanism as it sees fit.
 
+``login_manager.init_app(app)`` must be called before
+``auth.init_app(app)``.
+
+The currently logged-in user can be retrieved at
+``flask_login.current_user``, if any.
+
 
 Example for Simple Applications with Flask-Login Integration
 ------------------------------------------------------------
@@ -164,14 +218,14 @@ In your ``my_app.py``:
 
 ::
 
+    import flask_login
     from flask import Flask, request, redirect
     from flask_digest_auth import DigestAuth
-    from flask_login import LoginManager
 
     app: flask = Flask(__name__)
     ... (Configure the Flask application) ...
 
-    login_manager: LoginManager = LoginManager()
+    login_manager: flask_login.LoginManager = flask_login.LoginManager()
     login_manager.init_app(app)
 
     @login_manager.user_loader
@@ -186,9 +240,9 @@ In your ``my_app.py``:
         ... (Load the password hash) ...
 
     @app.get("/admin")
-    @login_manager.login_required
+    @flask_login.login_required
     def admin():
-        ... (Process the view) ...
+        return f"Hello, {flask_login.current_user.get_id()}!"
 
     @app.post("/logout")
     @flask_login.login_required
@@ -244,7 +298,7 @@ In your ``my_app/views.py``:
     @bp.get("/admin")
     @flask_login.login_required
     def admin():
-        ... (Process the view) ...
+        return f"Hello, {flask_login.current_user.get_id()}!"
 
     @app.post("/logout")
     @flask_login.login_required
@@ -288,14 +342,30 @@ 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
 =============
 
 You can write tests with our test client that handles HTTP Digest
-Authentication.  Example for a unittest testcase:
+Authentication.
+
+Example for a unittest_ test case:
 
 ::
 
+    from flask import Flask
     from flask_digest_auth import Client
     from flask_testing import TestCase
     from my_app import create_app
@@ -318,6 +388,41 @@ Authentication.  Example for a unittest testcase:
             self.assertEqual(response.status_code, 200)
 
 
+
+Example for a pytest_ test:
+
+::
+
+    import pytest
+    from flask import Flask
+    from flask_digest_auth import Client
+    from my_app import create_app
+
+    @pytest.fixture()
+    def app():
+        app: Flask = create_app({
+            "SECRET_KEY": token_urlsafe(32),
+            "TESTING": True
+        })
+        app.test_client_class = Client
+        yield app
+
+    @pytest.fixture()
+    def client(app):
+        return app.test_client()
+
+    def test_admin(app: Flask, client: Client):
+        with app.app_context():
+            response = self.client.get("/admin")
+            assert response.status_code == 401
+            response = self.client.get(
+                "/admin", digest_auth=("my_name", "my_pass"))
+            assert response.status_code == 200
+
+.. _unittest: https://docs.python.org/3/library/unittest.html
+.. _pytest: https://pytest.org
+
+
 Copyright
 =========
 
@@ -335,6 +440,7 @@ Copyright
  See the License for the specific language governing permissions and
  limitations under the License.
 
+
 Authors
 =======
 

setup.cfg

@@ -17,7 +17,7 @@
 
 [metadata]
 name = flask-digest-auth
-version = 0.1.1
+version = 0.2.1
 author = imacat
 author_email = imacat@mail.imacat.idv.tw
 description = The Flask HTTP Digest Authentication project.

src/flask_digest_auth/algo.py

@@ -61,6 +61,16 @@ def calc_response(
         cnonce or nc is missing with the auth or auth-int qop.
     """
 
+    def validate_required(field: t.Optional[str], error: str) -> None:
+        """Validates a required field.
+
+        :param field: The field that is required.
+        :param error: The error message.
+        :return: None.
+        """
+        if field is None:
+            raise UnauthorizedException(error)
+
     def calc_ha1() -> str:
         """Calculates and returns the first hash.
 
@@ -68,16 +78,13 @@ def calc_response(
         :raise UnauthorizedException: When the cnonce is missing with the MD5-sess
             algorithm.
         """
-        if algorithm is None or algorithm == "MD5":
-            return password_hash
         if algorithm == "MD5-sess":
-            if cnonce is None:
-                raise UnauthorizedException(
-                    f"Missing \"cnonce\" with algorithm=\"{algorithm}\"")
+            validate_required(
+                cnonce, f"Missing \"cnonce\" with algorithm=\"{algorithm}\"")
             return md5(f"{password_hash}:{nonce}:{cnonce}".encode("utf8")) \
                 .hexdigest()
-        raise UnauthorizedException(
-            f"Unsupported algorithm=\"{algorithm}\"")
+        # algorithm is None or algorithm == "MD5"
+        return password_hash
 
     def calc_ha2() -> str:
         """Calculates the second hash.
@@ -86,30 +93,20 @@ def calc_response(
         :raise UnauthorizedException: When the body is missing with
             qop="auth-int".
         """
-        if qop is None or qop == "auth":
-            return md5(f"{method}:{uri}".encode("utf8")).hexdigest()
         if qop == "auth-int":
-            if body is None:
-                raise UnauthorizedException(
-                    f"Missing \"body\" with qop=\"{qop}\"")
+            validate_required(body, f"Missing \"body\" with qop=\"{qop}\"")
             return md5(
                 f"{method}:{uri}:{md5(body).hexdigest()}".encode("utf8")) \
                 .hexdigest()
-        raise UnauthorizedException(f"Unsupported qop=\"{qop}\"")
+        # qop is None or qop == "auth"
+        return md5(f"{method}:{uri}".encode("utf8")).hexdigest()
 
     ha1: str = calc_ha1()
     ha2: str = calc_ha2()
-    if qop is None:
-        return md5(f"{ha1}:{nonce}:{ha2}".encode("utf8")).hexdigest()
     if qop == "auth" or qop == "auth-int":
-        if cnonce is None:
-            raise UnauthorizedException(
-                f"Missing \"cnonce\" with the qop=\"{qop}\"")
-        if nc is None:
-            raise UnauthorizedException(
-                f"Missing \"nc\" with the qop=\"{qop}\"")
+        validate_required(cnonce, f"Missing \"cnonce\" with the qop=\"{qop}\"")
+        validate_required(nc, f"Missing \"nc\" with the qop=\"{qop}\"")
         return md5(f"{ha1}:{nonce}:{nc}:{cnonce}:{qop}:{ha2}".encode("utf8"))\
             .hexdigest()
-    if cnonce is None:
-        raise UnauthorizedException(
-            f"Unsupported qop=\"{qop}\"")
+    # qop is None
+    return md5(f"{ha1}:{nonce}:{ha2}".encode("utf8")).hexdigest()

src/flask_digest_auth/auth.py

@@ -24,11 +24,9 @@ from __future__ import annotations
 import sys
 import typing as t
 from functools import wraps
-from random import random
-from secrets import token_urlsafe
+from secrets import token_urlsafe, randbits
 
-from flask import g, request, Response, session, abort, Flask, Request, \
-    current_app
+from flask import g, request, Response, session, abort, Flask, Request
 from itsdangerous import URLSafeTimedSerializer, BadData
 from werkzeug.datastructures import Authorization
 
@@ -36,6 +34,50 @@ from flask_digest_auth.algo import calc_response
 from flask_digest_auth.exception import UnauthorizedException
 
 
+class BasePasswordHashGetter:
+    """The base password hash getter."""
+
+    @staticmethod
+    def __call__(username: str) -> t.Optional[str]:
+        """Returns the password hash of a user.
+
+        :param username: The username.
+        :return: The password hash, or None if the user does not exist.
+        :raise UnboundLocalError: When the password hash getter function is
+            not registered yet.
+        """
+        raise UnboundLocalError("The function to return the password hash"
+                                " was not registered yet.")
+
+
+class BaseUserGetter:
+    """The base user getter."""
+
+    @staticmethod
+    def __call__(username: str) -> t.Optional[t.Any]:
+        """Returns a user.
+
+        :param username: The username.
+        :return: The user, or None if the user does not exist.
+        :raise UnboundLocalError: When the user getter function is not
+            registered yet.
+        """
+        raise UnboundLocalError("The function to return the user"
+                                " 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."""
 
@@ -52,9 +94,11 @@ class DigestAuth:
         self.use_opaque: bool = True
         self.domain: t.List[str] = []
         self.qop: t.List[str] = ["auth", "auth-int"]
-        self.__get_password_hash: t.Callable[[str], t.Optional[str]] \
-            = lambda x: None
-        self.__get_user: t.Callable[[str], t.Optional] = lambda x: None
+        self.app: t.Optional[Flask] = None
+        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.
@@ -66,6 +110,37 @@ class DigestAuth:
         class NoLogInException(Exception):
             """The exception thrown when the user is not authorized."""
 
+        def get_logged_in_user() -> t.Any:
+            """Returns the currently logged-in user.
+
+            :return: The currently logged-in user.
+            :raise NoLogInException: When the user is not logged in.
+            """
+            if "user" not in session:
+                raise NoLogInException
+            user: t.Optional[t.Any] = self.__get_user(session["user"])
+            if user is None:
+                del session["user"]
+                raise NoLogInException
+            return user
+
+        def auth_user(state: AuthState) -> t.Any:
+            """Authenticates a user.
+
+            :param state: The authentication state.
+            :return: The user.
+            :raise UnauthorizedException: When the authentication fails.
+            """
+            authorization: Authorization = request.authorization
+            if authorization is None:
+                raise UnauthorizedException
+            if authorization.type != "digest":
+                raise UnauthorizedException(
+                    "Not an HTTP digest authorization")
+            self.authenticate(state)
+            session["user"] = authorization.username
+            return self.__get_user(authorization.username)
+
         @wraps(view)
         def login_required_view(*args, **kwargs) -> t.Any:
             """The login-protected view.
@@ -75,34 +150,24 @@ class DigestAuth:
             :return: The response.
             """
             try:
-                if "user" not in session:
-                    raise NoLogInException
-                user: t.Optional[t.Any] = self.__get_user(session["user"])
-                if user is None:
-                    raise NoLogInException
-                g.user = user
+                g.user = get_logged_in_user()
                 return view(*args, **kwargs)
             except NoLogInException:
-                state: AuthState = AuthState()
-                authorization: Authorization = request.authorization
-                try:
-                    if authorization is None:
-                        raise UnauthorizedException
-                    if authorization.type != "digest":
-                        raise UnauthorizedException(
-                            "Not an HTTP digest authorization")
-                    self.authenticate(state)
-                    session["user"] = authorization.username
-                    g.user = self.__get_user(authorization.username)
-                    return view(*args, **kwargs)
-                except UnauthorizedException as e:
-                    if len(e.args) > 0:
-                        sys.stderr.write(e.args[0] + "\n")
-                    response: Response = Response()
-                    response.status = 401
-                    response.headers["WWW-Authenticate"] \
-                        = self.make_response_header(state)
-                    abort(response)
+                pass
+
+            state: AuthState = AuthState()
+            try:
+                g.user = auth_user(state)
+                self.__on_login(g.user)
+                return view(*args, **kwargs)
+            except UnauthorizedException as e:
+                if len(e.args) > 0:
+                    sys.stderr.write(e.args[0] + "\n")
+                response: Response = Response()
+                response.status = 401
+                response.headers["WWW-Authenticate"] \
+                    = self.make_response_header(state)
+                abort(response)
 
         return login_required_view
 
@@ -127,8 +192,8 @@ class DigestAuth:
             except BadData:
                 raise UnauthorizedException("Invalid opaque")
             state.opaque = authorization.opaque
-        password_hash: t.Optional[str] = self.__get_password_hash(
-            authorization.username)
+        password_hash: t.Optional[str] \
+            = self.__get_password_hash(authorization.username)
         if password_hash is None:
             raise UnauthorizedException(
                 f"No such user \"{authorization.username}\"")
@@ -157,11 +222,22 @@ class DigestAuth:
         :param state: The authorization state.
         :return: The WWW-Authenticate response header.
         """
-        opaque: t.Optional[str] = None if not self.use_opaque else \
-            (state.opaque if state.opaque is not None
-             else self.serializer.dumps(random(), salt="opaque"))
+
+        def get_opaque() -> t.Optional[str]:
+            """Returns the opaque value.
+
+            :return: The opaque value.
+            """
+            if not self.use_opaque:
+                return None
+            if state.opaque is not None:
+                return state.opaque
+            return self.serializer.dumps(randbits(32), salt="opaque")
+
+        opaque: t.Optional[str] = get_opaque()
         nonce: str = self.serializer.dumps(
-            random(), salt="nonce" if opaque is None else f"nonce-{opaque}")
+            randbits(32),
+            salt="nonce" if opaque is None else f"nonce-{opaque}")
 
         header: str = f"Digest realm=\"{self.realm}\""
         if len(self.domain) > 0:
@@ -187,7 +263,20 @@ class DigestAuth:
             hash, or None if the user does not exist.
         :return: None.
         """
-        self.__get_password_hash = func
+
+        class PasswordHashGetter(BasePasswordHashGetter):
+            """The base password hash getter."""
+
+            @staticmethod
+            def __call__(username: str) -> t.Optional[str]:
+                """Returns the password hash of a user.
+
+                :param username: The username.
+                :return: The password hash, or None if the user does not exist.
+                """
+                return func(username)
+
+        self.__get_password_hash = PasswordHashGetter()
 
     def register_get_user(self, func: t.Callable[[str], t.Optional[t.Any]])\
             -> None:
@@ -197,7 +286,41 @@ class DigestAuth:
             or None if the user does not exist.
         :return: None.
         """
-        self.__get_user = func
+
+        class UserGetter(BaseUserGetter):
+            """The user getter."""
+
+            @staticmethod
+            def __call__(username: str) -> t.Optional[t.Any]:
+                """Returns a user.
+
+                :param username: The username.
+                :return: The user, or None if the user does not exist.
+                """
+                return func(username)
+
+        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.
@@ -205,13 +328,12 @@ class DigestAuth:
         :param app: The Flask application.
         :return: None.
         """
+        app.digest_auth = self
+        self.app = app
 
-        try:
+        if hasattr(app, "login_manager"):
             from flask_login import LoginManager, login_user
 
-            if not hasattr(app, "login_manager"):
-                raise AttributeError(
-                    "Please run the Flask-Login init-app() first")
             login_manager: LoginManager = getattr(app, "login_manager")
 
             @login_manager.unauthorized_handler
@@ -246,18 +368,14 @@ 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) != "":
                         app.logger.warning(str(e))
                     return None
 
-        except ModuleNotFoundError:
-            raise ModuleNotFoundError(
-                "init_app() is only for Flask-Login integration")
-
-    @staticmethod
-    def logout() -> None:
+    def logout(self) -> None:
         """Logs out the user.
         This actually causes the next authentication to fail, which forces
         the browser to ask the user for the username and password again.
@@ -267,7 +385,7 @@ class DigestAuth:
         if "user" in session:
             del session["user"]
         try:
-            if hasattr(current_app, "login_manager"):
+            if hasattr(self.app, "login_manager"):
                 from flask_login import logout_user
                 logout_user()
         except ModuleNotFoundError:

src/flask_digest_auth/test.py

@@ -66,9 +66,8 @@ class Client(WerkzeugClient):
         :return: The request authorization.
         """
         qop: t.Optional[t.Literal["auth", "auth-int"]] = None
-        if www_authenticate.qop is not None:
-            if "auth" in www_authenticate.qop:
-                qop = "auth"
+        if www_authenticate.qop is not None and "auth" in www_authenticate.qop:
+            qop = "auth"
 
         cnonce: t.Optional[str] = None
         if qop is not None or www_authenticate.algorithm == "MD5-sess":

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 +32,21 @@ _USERNAME: str = "Mufasa"
 _PASSWORD: str = "Circle Of Life"
 
 
+class User:
+    """A dummy user"""
+
+    def __init__(self, username: str, password: str):
+        """Constructs a dummy user.
+
+        :param username: The username.
+        :param password: The clear-text password.
+        """
+        self.username: str = username
+        self.password_hash: str = make_password_hash(
+            _REALM, username, password)
+        self.visits: int = 0
+
+
 class AuthenticationTestCase(TestCase):
     """The test case for the HTTP digest authentication."""
 
@@ -49,8 +63,9 @@ class AuthenticationTestCase(TestCase):
         app.test_client_class = Client
 
         auth: DigestAuth = DigestAuth(realm=_REALM)
-        user_db: t.Dict[str, str] \
-            = {_USERNAME: make_password_hash(_REALM, _USERNAME, _PASSWORD)}
+        auth.init_app(app)
+        self.user: User = User(_USERNAME, _PASSWORD)
+        user_db: t.Dict[str, User] = {_USERNAME: self.user}
 
         @auth.register_get_password
         def get_password_hash(username: str) -> t.Optional[str]:
@@ -59,7 +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]:
@@ -68,8 +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
@@ -117,6 +141,7 @@ class AuthenticationTestCase(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.data.decode("UTF-8"),
                          f"Hello, {_USERNAME}! #2")
+        self.assertEqual(self.user.visits, 1)
 
     def test_stale_opaque(self) -> None:
         """Tests the stale and opaque value.
@@ -193,3 +218,4 @@ class AuthenticationTestCase(TestCase):
 
         response = self.client.get(admin_uri)
         self.assertEqual(response.status_code, 200)
+        self.assertEqual(self.user.visits, 2)

tests/test_flask_login.py

@@ -35,12 +35,16 @@ _PASSWORD: str = "Circle Of Life"
 class User:
     """A dummy user."""
 
-    def __init__(self, username: str):
+    def __init__(self, username: str, password: str):
         """Constructs a dummy user.
 
         :param username: The username.
+        :param password: The clear-text password.
         """
         self.username: str = username
+        self.password_hash: str = make_password_hash(
+            _REALM, username, password)
+        self.visits: int = 0
         self.is_authenticated: bool = True
         self.is_active: bool = True
         self.is_anonymous: bool = False
@@ -82,8 +86,8 @@ 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)}
+        self.user: User = User(_USERNAME, _PASSWORD)
+        user_db: t.Dict[str, User] = {_USERNAME: self.user}
 
         @auth.register_get_password
         def get_password_hash(username: str) -> t.Optional[str]:
@@ -92,7 +96,17 @@ 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 +115,7 @@ 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
@@ -110,7 +124,7 @@ class FlaskLoginTestCase(TestCase):
 
             :return: The response.
             """
-            return f"Hello, {flask_login.current_user.username}! #1"
+            return f"Hello, {flask_login.current_user.get_id()}! #1"
 
         @app.get("/admin-2/auth", endpoint="admin-2")
         @flask_login.login_required
@@ -119,7 +133,7 @@ class FlaskLoginTestCase(TestCase):
 
             :return: The response.
             """
-            return f"Hello, {flask_login.current_user.username}! #2"
+            return f"Hello, {flask_login.current_user.get_id()}! #2"
 
         @app.post("/logout", endpoint="logout")
         @flask_login.login_required
@@ -139,7 +153,7 @@ class FlaskLoginTestCase(TestCase):
         :return: None.
         """
         if not self.has_flask_login:
-            self.skipTest("Skipped testing Flask-Login integration without it.")
+            self.skipTest("Skipped without Flask-Login.")
 
         response: Response = self.client.get(self.app.url_for("admin-1"))
         self.assertEqual(response.status_code, 401)
@@ -152,6 +166,7 @@ class FlaskLoginTestCase(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.data.decode("UTF-8"),
                          f"Hello, {_USERNAME}! #2")
+        self.assertEqual(self.user.visits, 1)
 
     def test_stale_opaque(self) -> None:
         """Tests the stale and opaque value.
@@ -159,7 +174,7 @@ class FlaskLoginTestCase(TestCase):
         :return: None.
         """
         if not self.has_flask_login:
-            self.skipTest("Skipped testing Flask-Login integration without it.")
+            self.skipTest("Skipped without Flask-Login.")
 
         admin_uri: str = self.app.url_for("admin-1")
         response: Response
@@ -206,6 +221,9 @@ class FlaskLoginTestCase(TestCase):
 
         :return: None.
         """
+        if not self.has_flask_login:
+            self.skipTest("Skipped without Flask-Login.")
+
         admin_uri: str = self.app.url_for("admin-1")
         logout_uri: str = self.app.url_for("logout")
         response: Response
@@ -237,3 +255,4 @@ class FlaskLoginTestCase(TestCase):
 
         response = self.client.get(admin_uri)
         self.assertEqual(response.status_code, 200)
+        self.assertEqual(self.user.visits, 2)