# The Flask HTTP Digest Authentication Project.
# Author: imacat@mail.imacat.idv.tw (imacat), 2022/10/22
# Copyright (c) 2022 imacat.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""The HTTP Digest Authentication.
See RFC 2617 HTTP Authentication: Basic and Digest Access Authentication
"""
from __future__ import annotations
import sys
import typing as t
from functools import wraps
from secrets import token_urlsafe, randbits
from flask import g, request, Response, session, abort, Flask, Request
from itsdangerous import URLSafeTimedSerializer, BadData
from werkzeug.datastructures import Authorization
from flask_digest_auth.algo import calc_response
class DigestAuth:
"""The HTTP digest authentication."""
def __init__(self, realm: t.Optional[str] = None):
"""Constructs the HTTP digest authentication.
:param realm: The realm.
"""
self.secret_key: str = token_urlsafe(32)
self.serializer: URLSafeTimedSerializer \
= URLSafeTimedSerializer(self.secret_key)
self.realm: str = "" if realm is None else realm
self.algorithm: t.Optional[str] = None
self.use_opaque: bool = True
self.domain: t.List[str] = []
self.qop: t.List[str] = ["auth", "auth-int"]
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.
For example:
::
@auth.login_required
def admin():
return f"Hello, {g.user.username}!"
The logged-in user can be retrieved at ``g.user``.
:param view: The view.
:return: The login-protected view.
"""
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.
:param args: The positional arguments of the view.
:param kwargs: The keyword arguments of the view.
:return: The response.
"""
try:
g.user = get_logged_in_user()
return view(*args, **kwargs)
except NoLogInException:
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
def __authenticate(self, state: AuthState) -> None:
"""Authenticate a user.
:param state: The authorization state.
:return: None.
:raise UnauthorizedException: When the authentication failed.
"""
if "digest_auth_logout" in session:
del session["digest_auth_logout"]
raise UnauthorizedException("Logging out")
authorization: Authorization = request.authorization
if self.use_opaque:
if authorization.opaque is None:
raise UnauthorizedException(
"Missing \"opaque\" in the Authorization header")
try:
self.serializer.loads(
authorization.opaque, salt="opaque", max_age=1800)
except BadData:
raise UnauthorizedException("Invalid opaque")
state.opaque = authorization.opaque
password_hash: t.Optional[str] \
= self.__get_password_hash(authorization.username)
if password_hash is None:
raise UnauthorizedException(
f"No such user \"{authorization.username}\"")
expected: str = calc_response(
method=request.method, uri=authorization.uri,
password_hash=password_hash, nonce=authorization.nonce,
qop=authorization.qop,
algorithm=authorization.get("algorithm"),
cnonce=authorization.cnonce, nc=authorization.nc,
body=request.data)
if authorization.response != expected:
state.stale = False
raise UnauthorizedException("Incorrect response value")
try:
self.serializer.loads(
authorization.nonce,
salt="nonce" if authorization.opaque is None
else f"nonce-{authorization.opaque}")
except BadData:
state.stale = True
raise UnauthorizedException("Invalid nonce")
def __make_response_header(self, state: AuthState) -> str:
"""Composes and returns the ``WWW-Authenticate`` response header.
:param state: The authorization state.
:return: The ``WWW-Authenticate`` response header.
"""
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(
randbits(32),
salt="nonce" if opaque is None else f"nonce-{opaque}")
header: str = f"Digest realm=\"{self.realm}\""
if len(self.domain) > 0:
domain_list: str = ",".join(self.domain)
header += f", domain=\"{domain_list}\""
header += f", nonce=\"{nonce}\""
if opaque is not None:
header += f", opaque=\"{opaque}\""
if state.stale is not None:
header += f", stale=TRUE" if state.stale else f", stale=FALSE"
if self.algorithm is not None:
header += f", algorithm=\"{self.algorithm}\""
if len(self.qop) > 0:
qop_list: str = ",".join(self.qop)
header += f", qop=\"{qop_list}\""
return header
def register_get_password(self, func: t.Callable[[str], t.Optional[str]])\
-> None:
"""The decorator to register the callback to obtain the password hash.
For example:
::
@auth.register_get_password
def get_password_hash(username: str) -> Optional[str]:
user = User.query.filter(User.username == username).first()
return None if user is None else user.password
:param func: The callback that given the username, returns the password
hash, or None if the user does not exist.
:return: None.
"""
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:
"""The decorator to register the callback to obtain the user.
For example:
::
@auth.register_get_user
def get_user(username: str) -> Optional[User]:
return User.query.filter(User.username == username).first()
:param func: The callback that given the username, returns the user,
or None if the user does not exist.
:return: None.
"""
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:
"""The decorator to register the callback to run when the user logs in.
For example:
::
@auth.register_on_login
def on_login(user: User) -> None:
user.visits = user.visits + 1
: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.
For example:
::
app: flask = Flask(__name__)
auth: DigestAuth = DigestAuth()
auth.realm = "My Admin"
auth.init_app(app)
:param app: The Flask application.
:return: None.
"""
app.digest_auth = self
self.app = app
if hasattr(app, "login_manager"):
from flask_login import LoginManager, login_user
login_manager: LoginManager = getattr(app, "login_manager")
@login_manager.unauthorized_handler
def unauthorized() -> None:
"""Handles when the user is unauthorized.
:return: None.
"""
response: Response = Response()
response.status = 401
response.headers["WWW-Authenticate"] \
= self.__make_response_header(g.digest_auth_state)
abort(response)
@login_manager.request_loader
def load_user_from_request(req: Request) -> t.Optional[t.Any]:
"""Loads the user from the request header.
:param req: The request.
:return: The authenticated user, or None if the
authentication fails
"""
g.digest_auth_state = AuthState()
authorization: Authorization = req.authorization
try:
if authorization is None:
raise UnauthorizedException
if authorization.type != "digest":
raise UnauthorizedException(
"Not an HTTP digest authorization")
self.__authenticate(g.digest_auth_state)
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
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.
For example:
::
@app.post("/logout")
@auth.login_required
def logout():
auth.logout()
return redirect(request.form.get("next"))
:return: None.
"""
if "user" in session:
del session["user"]
try:
if hasattr(self.app, "login_manager"):
from flask_login import logout_user
logout_user()
except ModuleNotFoundError:
pass
session["digest_auth_logout"] = True
class AuthState:
"""The authorization state."""
def __init__(self):
"""Constructs the authorization state."""
self.opaque: t.Optional[str] = None
self.stale: t.Optional[bool] = None
class UnauthorizedException(Exception):
"""The exception thrown when the authentication is failed."""
pass
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.
"""