用 Flask 来写个轻博客 (25) — 使用 Flask-Principal 实现角色权限功能

Blog 项目源码：https://github.com/JmilkFan/JmilkFan-s-Blog

前文列表

扩展阅读

Flask Principal — Flask Principal 0.4.0 documentation
Flask-Login — Flask-Login 0.4.0 documentation

Flask-Principal

Flask-Principal 是一个 Flask 扩展(用户权限框架), 框架主要部分包含身份(Identity)，需求(Needs)，权限(Permission)，和包含身份信息的上下文环境(IdentityContext)。

Flask 中的每一个 user 都会拥有一种 Identity, 而每一种 Identity 又会被关联到一个 Needs. Flask-Principal 提供了两种 Needs(RoleNeed/UserNeed). Needs 本质上是一个 namedtuple(具名元组) EG. ("role", "admin"), 其定义了在这个 Identity 能做什么事情. 也就是说 Permission 其实是通过 Needs 来定义和初始化的, 其中 Permission 可以是一个权限的集合.

这里写图片描述

除此之外, Flask-Principal 是通过信号(signal)来与 Flask 应用进行交互的，满足了低耦合的理念。其定义了两个重要的signal：

identity_changed：一般在用户身份变化时发送该信号, 在用户登录认证成功后，通过发送 identity_changed 信号告知 Flask-Principal 用户登录成功, 需要对用户的权限进行改变
identity_loaded：一般在用户权限需要被载入时发送该信息. 通常在用户身份改变时, 就需要载入相应的权限.

使用 Flask-Principal 来实现角色权限功能

添加 Role Model

而且 Role 和 User 应该是 many to many 的关系.

models.py

users_roles = db.Table('users_roles',
    db.Column('user_id', db.String(45), db.ForeignKey('users.id')),
    db.Column('role_id', db.String(45), db.ForeignKey('roles.id')))


class User(db.Model):
    """Represents Proected users."""

    # Set the name for table
    __tablename__ = 'users'
    id = db.Column(db.String(45), primary_key=True)
    username = db.Column(db.String(255))
    password = db.Column(db.String(255))
    # one to many: User ==> Post 
    # Establish contact with Post's ForeignKey: user_id
    posts = db.relationship(
        'Post',
        backref='users',
        lazy='dynamic')

    roles = db.relationship(
        'Role',
        secondary=users_roles,
        backref=db.backref('users', lazy='dynamic'))

    def __init__(self, id, username, password):
        self.id = id
        self.username = username
        self.password = self.set_password(password)

        # Setup the default-role for user.
        default = Role.query.filter_by(name="default").one()
        self.roles.append(default)

    def __repr__(self):
        """Define the string format for instance of User."""
        return "<Model User `{}`>".format(self.username)

    def set_password(self, password):
        """Convert the password to cryptograph via flask-bcrypt"""
        return bcrypt.generate_password_hash(password)

    def check_password(self, password):
        return bcrypt.check_password_hash(self.password, password)

    def is_authenticated(self):
        """Check the user whether logged in."""

        # Check the User's instance whether Class AnonymousUserMixin's instance.
        if isinstance(self, AnonymousUserMixin):
            return False
        else:
            return True

    def is_active():
        """Check the user whether pass the activation process."""

        return True

    def is_anonymous(self):
        """Check the user's login status whether is anonymous."""

        if isinstance(self, AnonymousUserMixin):
            return True
        else:
            return False

    def get_id(self):
        """Get the user's uuid from database."""

        return unicode(self.id)


class Role(db.Model):
    """Represents Proected roles."""
    __tablename__ = 'roles'

    id = db.Column(db.String(45), primary_key=True)
    name = db.Column(db.String(255), unique=True)
    description = db.Column(db.String(255))

    def __init__(self, id, name):
        self.id = id
        self.name = name

    def __repr__(self):
        return "<Model Role `{}`>".format(self.name)

NOTE: 这样的话我们可以为 user 指定一个 role 集. 用来代表该用户所拥有的 Identity, 这也是之后为 user 对象绑定 Needs 所需要的前提.

在 Manager shell 中手动的添加角色

创建 roles 数据表

(env) jmilkfan@JmilkFan-Devstack:/opt/JmilkFan-s-Blog$ python manage.py shell
>>> db.create_all()

创建新用户

>>> from uuid import uuid4
>>> user = User(id=str(uuid4()), username='jmilkfan_2016', password="fanguiju")
>>> db.session.add(user)
>>> db.session.commit()

创建新角色并与新用户建立关联

>>> role_admin = Role(id=str(uuid4()), name="admin")
>>> role_poster = Role(id=str(uuid4()), name="poster")
>>> role_default = Role(id=str(uuid4()), name="default")

>>> user
<Model User `jmilkfan_2016`>
>>> role_admin.users = [user]
>>> role_poster.users = [user]
>>> db.session.add(role_admin)
>>> db.session.add(role_poster)
>>> db.session.add(role_default)
>>> db.session.commit()

初始化 Flask-Principal 和 Permission

extensions.py

from flask.ext.principal import Principal, Permission, RoleNeed


# Create the Flask-Principal's instance
principals = Principal()

# 这里设定了 3 种权限, 这些权限会被绑定到 Identity 之后才会发挥作用.
# Init the role permission via RoleNeed(Need).
admin_permission = Permission(RoleNeed('admin'))
poster_permission = Permission(RoleNeed('poster'))
default_permission = Permission(RoleNeed('default'))

实现权限载入信号逻辑

jmilkfannsblog.__init__.py

def create_app(object_name):
    """Create the app instance via `Factory Method`"""

    app = Flask(__name__)
    # Set the config for app instance
    app.config.from_object(object_name)

    # Will be load the SQLALCHEMY_DATABASE_URL from config.py to db object
    db.init_app(app)
    # Init the Flask-Bcrypt via app object
    bcrypt.init_app(app)
    # Init the Flask-OpenID via app object
    openid.init_app(app)
    # Init the Flask-Login via app object
    login_manager.init_app(app)
    # Init the Flask-Prinicpal via app object
    principals.init_app(app)

    @identity_loaded.connect_via(app)
    def on_identity_loaded(sender, identity):
        """Change the role via add the Need object into Role.

           Need the access the app object.
        """

        # Set the identity user object
        identity.user = current_user

        # Add the UserNeed to the identity user object
        if hasattr(current_user, 'id'):
            identity.provides.add(UserNeed(current_user.id))

        # Add each role to the identity user object
        if hasattr(current_user, 'roles'):
            for role in current_user.roles:
                identity.provides.add(RoleNeed(role.name))

    # Register the Blueprint into app object
    app.register_blueprint(blog.blog_blueprint)
    app.register_blueprint(main.main_blueprint)

    return app

NOTE 1: 因为 identity_loaded 信号实现函数,需要访问 app 对象, 所以直接在 __init\_\_.create_app() 中实现.
NOTE 2: on_identity_loaded() 函数在用户身份发生了变化, 需要重载权限的时候被调用. 首先将当前的用户绑定到一个 Identity 的实例化对象中, 然后将该用户 id 的 UserNeed 和该用户所拥有的 roles 对应的 RoleNeed 绑定到该 Identity 中. 实现了将数据库中 user 所拥有的 roles 都以 Needs 的形式绑定到其自身中.

实现身份改变信号逻辑

jmilkfsnsblog.controllers.main.py

from flask.ext.principal import Identity, AnonymousIdentity, identity_changed, current_app


@main_blueprint.route('/login', methods=['GET', 'POST'])
@openid.loginhandler
def login():
    """View function for login.

       Flask-OpenID will be receive the Authentication-information
       from relay party.
    """
...

    # Will be check the account whether rigjt.
    if form.validate_on_submit():

        # Using session to check the user's login status
        # Add the user's name to cookie.
        # session['username'] = form.username.data

        user = User.query.filter_by(username=form.username.data).one()

        # Using the Flask-Login to processing and check the login status for user
        # Remember the user's login status. 
        login_user(user, remember=form.remember.data)

        identity_changed.send(
            current_app._get_current_object(),
            identity=Identity(user.id))

        flash("You have been logged in.", category="success")
        return redirect(url_for('blog.home'))

...

NOTE 1: identity_changed一般在用户的身份发生变化时发送, 所以我们一般选择 login()视图函数中实现.
NOTE 2: identity_changed.send() 函数会将 sender: current_app._get_current_object() 当前应用对象 app 和身份对象 identity: Identity(user.id) 当前要登录的用户对象, 以信号的新式发送出去, 表示应用 app 对象中的 user 用户对象的 identity 被改变了.
NOTE 3: 在 identity_changed 信息被发送之后, 被装饰器 identity_loaded.connect_via(app) 装饰的函数 on_identity_loaded(sender, identity) 就会接受该信号, 并为 user 绑定应有 Needs, 以此来赋予其权限.

NOTE 4: 在用户认证通过后，Flask-Principal 会将用户的身份(identity) 存储在 session 中。

除了登录的时候用户身份会被改变, 登出也是一样的.

@main_blueprint.route('/logout', methods=['GET', 'POST'])
def logout():
    """View function for logout."""

    # Remove the username from the cookie.
    # session.pop('username', None)

    # Using the Flask-Login to processing and check the logout status for user.
    logout_user()

    identity_changed.send(
        current_app._get_current_object(),
        identity=AnonymousIdentity())
    flash("You have been logged out.", category="success")
    return redirect(url_for('main.login'))

NOTE: 用户登出系统后清理 session，Flask-Principal 会将用户的身份变为 AnonymousIdentity(匿名身份)。

实现只有文章作者才能编辑文章

jmilkfansblog.controllers.blog.py

@blog_blueprint.route('/edit/<string:id>', methods=['GET', 'POST'])
@login_required
@poster_permission.require(http_exception=403)
def edit_post(id):
    """View function for edit_post."""

    post = Post.query.get_or_404(id)

    # Ensure the user logged in.
    if not current_user:
        return redirect(url_for('main.login'))

    # Only the post onwer can be edit this post.
    if current_user != post.users:
        return redirect(url_for('blog.post', post_id=id))

    # 当 user 是 poster 或者 admin 时, 才能够编辑文章
    # Admin can be edit the post.
    permission = Permission(UserNeed(post.users.id))
    if permission.can() or admin_permission.can():
        form = PostForm()

        #if current_user != post.users:
        #    abort(403)

        if form.validate_on_submit():
            post.title = form.title.data
            post.text = form.text.data
            post.publish_date = datetime.now()

            # Update the post
            db.session.add(post)
            db.session.commit()

            return redirect(url_for('blog.post', post_id=post.id))
    else:
        abort(403)

    # Still retain the original content, if validate is false.
    form.title.data = post.title
    form.text.data = post.text
    return render_template('edit_post.html', form=form, post=post)

实现效果

以具有 poster identity 的 jmilkfan_2016 登录
创建新的文章
在 jmilkfansblog.controllers.blog:edit_port()中打个断点, 我们来看看此时 permision 和 admin_permission 对象的值.

(Pdb) l
165             return redirect(url_for('blog.post', post_id=id))
166     
167         import pdb
168         pdb.set_trace()
169         # Admin can be edit the post.
170  ->     permission = Permission(UserNeed(post.users.id))
171         if permission.can() or admin_permission.can():
172             form = PostForm()
173     
174             #if current_user != post.users:
175             #    abort(403)
(Pdb) n
> /opt/JmilkFan-s-Blog/jmilkfansblog/controllers/blog.py(171)edit_post()
-> if permission.can() or admin_permission.can():
(Pdb) permission
<Permission needs=set([Need(method='id', value=u'b003f813-abfa-46d6-babc-2033b0b43f7e')]) excludes=set([])>
(Pdb) permission.can()
True

可以看见 permission 对象所对应的 user id == b003f813-abfa-46d6-babc-2033b0b43f7e, 而该 user 在数据库中对应的 roles == [87d180cc-bfa5-4c6a-87d4-01decb9c8649, 4b8b5c13-76fa-47e1-8403-623d284b2db7], 所以 user 在登录时由于其自身 Identity 的改变而触发了 on_identity_loaded() 方法, 将 admin/poster 两个 roles 对应的 RoleNeed 绑定到 user 自身的 identity 对象上, 从而拥有了编辑文章的权限.