class LoginManager:
    def __init__(self, app=None, add_context_processor=True):
        #: A class or factory function that produces an anonymous user, which
        #: is used when no one is logged in.
        self.anonymous_user = AnonymousUserMixin
        #: The name of the view to redirect to when the user needs to log in.
        #: (This can be an absolute URL as well, if your authentication
        #: machinery is external to your application.)
        self.login_view = None
        #: Names of views to redirect to when the user needs to log in,
        #: per blueprint. If the key value is set to None the value of
        #: :attr:`login_view` will be used instead.
        self.blueprint_login_views = {}
        #: The message to flash when a user is redirected to the login page.
        self.login_message = LOGIN_MESSAGE
        #: The message category to flash when a user is redirected to the login
        #: page.
        self.login_message_category = LOGIN_MESSAGE_CATEGORY
        #: The name of the view to redirect to when the user needs to
        #: reauthenticate.
        self.refresh_view = None
        #: The message to flash when a user is redirected to the 'needs
        #: refresh' page.
        self.needs_refresh_message = REFRESH_MESSAGE
        #: The message category to flash when a user is redirected to the
        #: 'needs refresh' page.
        self.needs_refresh_message_category = REFRESH_MESSAGE_CATEGORY
        #: The mode to use session protection in. This can be either
        #: ``'basic'`` (the default) or ``'strong'``, or ``None`` to disable
        #: it.
        self.session_protection = "basic"
		......

def user_loader(self, callback):
        """
        This sets the callback for reloading a user from the session. The
        function you set should take a user ID (a ``str``) and return a
        user object, or ``None`` if the user does not exist.
        :param callback: The callback for retrieving a user object.
        :type callback: callable
        """
        self._user_callback = callback
        return self.

@login_manager.user_loader
def load_user(userid):
    return User.get(userid)

import flask
app = flask.Flask(__name__)
app.secret_key = 'super secret string'  # Change this!

import flask_login
login_manager = flask_login.LoginManager() # 初始化一個 LoginManager 類對象
login_manager.login_view = 'login'
login_manager.login_message_category = 'info'
login_manager.login_message = 'Access denied.'
login_manager.init_app(app) # 配置該對象

# Our mock database.
users = {'foo@bar.tld': {'password': 'secret'}}

class User(flask_login.UserMixin):
    pass
@login_manager.user_loader
def user_loader(email):
    if email not in users:
        return
    user = User()
    user.id = email
    return user
@login_manager.request_loader
def request_loader(request):
    email = request.form.get('email')
    if email not in users:
        return
    user = User()
    user.id = email
    return user

@app.route('/login', methods=['GET', 'POST'])
def login():
    if flask.request.method == 'GET':
        return '''
               <form action='login' method='POST'>
                <input type='text' name='email' id='email' placeholder='email'/>
                <input type='password' name='password' id='password' placeholder='password'/>
                <input type='submit' name='submit'/>
               </form>
               '''
    email = flask.request.form['email']
    if email in users and flask.request.form['password'] == users[email]['password']:
        user = User()
        user.id = email
        flask_login.login_user(user)
        return flask.redirect(flask.url_for('protected'))
    return 'Bad login'
@app.route('/protected')
@flask_login.login_required
def protected():
    return 'Logged in as: ' + flask_login.current_user.id

@app.route('/logout')
def logout():
    flask_login.logout_user()
    return 'Logged out'

@login_manager.unauthorized_handler
def unauthorized_handler():
    return 'Unauthorized', 401