Adding authorization¶

Pyramid provides facilities for authentication and authorization. We'll make use of both features to provide security to our application. Our application currently allows anyone with access to the server to view, edit, and add pages to our wiki. We'll change that to allow only people who are members of a group named group:editors to add and edit wiki pages, but we'll continue allowing anyone with access to the server to view pages.

We will also add a login page and a logout link on all the pages. The login page will be shown when a user is denied access to any of the views that require permission, instead of a default "403 Forbidden" page.

We will implement the access control with the following steps:

Add password hashing dependencies.
Add users and groups (security.py, a new module).
Add an ACL (models.py).
Add an authentication policy and an authorization policy (__init__.py).
Add permission declarations to the edit_page and add_page views (views.py).

Then we will add the login and logout features:

Add login and logout views (views.py).
Add a login template (login.pt).
Make the existing views return a logged_in flag to the renderer (views.py).
Add a "Logout" link to be shown when logged in and viewing or editing a page (view.pt, edit.pt).

Access control¶

Add dependencies¶

Just like in Defining Views, we need a new dependency. We need to add the bcrypt package, to our tutorial package's setup.py file by assigning this dependency to the requires parameter in the setup() function.

Open setup.py and edit it to look like the following:

import os

from setuptools import setup, find_packages

here = os.path.abspath(os.path.dirname(__file__))
with open(os.path.join(here, 'README.txt')) as f:
    README = f.read()
with open(os.path.join(here, 'CHANGES.txt')) as f:
    CHANGES = f.read()

requires = [
    'plaster_pastedeploy',
    'pyramid >= 1.9a',
    'pyramid_chameleon',
    'pyramid_debugtoolbar',
    'pyramid_retry',
    'pyramid_tm',
    'pyramid_zodbconn',
    'transaction',
    'ZODB3',
    'waitress',
    'docutils',
    'bcrypt',
]

tests_require = [
    'WebTest >= 1.3.1',  # py3 compat
    'pytest>=3.7.4',
    'pytest-cov',
]

setup(
    name='tutorial',
    version='0.0',
    description='myproj',
    long_description=README + '\n\n' + CHANGES,
    classifiers=[
        'Programming Language :: Python',
        'Framework :: Pyramid',
        'Topic :: Internet :: WWW/HTTP',
        'Topic :: Internet :: WWW/HTTP :: WSGI :: Application',
    ],
    author='',
    author_email='',
    url='',
    keywords='web pyramid pylons',
    packages=find_packages(),
    include_package_data=True,
    zip_safe=False,
    extras_require={
        'testing': tests_require,
    },
    install_requires=requires,
    entry_points={
        'paste.app_factory': [
            'main = tutorial:main',
        ],
    },
)

Only the highlighted line needs to be added.

Do not forget to run pip install -e . just like in Running pip install -e ..

Note

We are using the bcrypt package from PyPI to hash our passwords securely. There are other one-way hash algorithms for passwords if bcrypt is an issue on your system. Just make sure that it's an algorithm approved for storing passwords versus a generic one-way hash.

Add users and groups¶

Create a new tutorial/security.py module with the following content:

import bcrypt


def hash_password(pw):
    hashed_pw = bcrypt.hashpw(pw.encode('utf-8'), bcrypt.gensalt())
    # return unicode instead of bytes because databases handle it better
    return hashed_pw.decode('utf-8')

def check_password(expected_hash, pw):
    if expected_hash is not None:
        return bcrypt.checkpw(pw.encode('utf-8'), expected_hash.encode('utf-8'))
    return False

USERS = {'editor': hash_password('editor'),
          'viewer': hash_password('viewer')}
GROUPS = {'editor':['group:editors']}

def groupfinder(userid, request):
    if userid in USERS:
        return GROUPS.get(userid, [])

The groupfinder function accepts a userid and a request and returns one of these values:

If userid exists in the system, it will return a sequence of group identifiers (or an empty sequence if the user isn't a member of any groups).
If the userid does not exist in the system, it will return None.

For example, groupfinder('editor', request ) returns ['group:editor'], groupfinder('viewer', request) returns [], and groupfinder('admin', request) returns None. We will use groupfinder() as an authentication policy "callback" that will provide the principal or principals for a user.

There are two helper methods that will help us later to authenticate users. The first is hash_password which takes a raw password and transforms it using bcrypt into an irreversible representation, a process known as "hashing". The second method, check_password, will allow us to compare the hashed value of the submitted password against the hashed value of the password stored in the user's record. If the two hashed values match, then the submitted password is valid, and we can authenticate the user.

We hash passwords so that it is impossible to decrypt and use them to authenticate in the application. If we stored passwords foolishly in clear text, then anyone with access to the database could retrieve any password to authenticate as any user.

In a production system, user and group data will most often be saved and come from a database, but here we use "dummy" data to represent user and groups sources.

Add an ACL¶

Open tutorial/models.py and add the following import statement near the top:

from pyramid.security import (
    Allow,
    Everyone,
    )

Add the following lines to the Wiki class:

class Wiki(PersistentMapping):
    __name__ = None
    __parent__ = None
    __acl__ = [ (Allow, Everyone, 'view'),
                (Allow, 'group:editors', 'edit') ]

We import Allow, an action that means that permission is allowed, and Everyone, a special principal that is associated to all requests. Both are used in the ACE entries that make up the ACL.

The ACL is a list that needs to be named __acl__ and be an attribute of a class. We define an ACL with two ACE entries: the first entry allows any user the view permission. The second entry allows the group:editors principal the edit permission.

The Wiki class that contains the ACL is the resource constructor for the root resource, which is a Wiki instance. The ACL is provided to each view in the context of the request as the context attribute.

It's only happenstance that we're assigning this ACL at class scope. An ACL can be attached to an object instance too; this is how "row level security" can be achieved in Pyramid applications. We actually need only one ACL for the entire system, however, because our security requirements are simple, so this feature is not demonstrated. See Assigning ACLs to Your Resource Objects for more information about what an ACL represents.

Add authentication and authorization policies¶

Open tutorial/__init__.py and add the highlighted import statements:

from pyramid.config import Configurator
from pyramid_zodbconn import get_connection

from pyramid.authentication import AuthTktAuthenticationPolicy
from pyramid.authorization import ACLAuthorizationPolicy

from .models import appmaker
from .security import groupfinder

Now add those policies to the configuration:

    settings['tm.manager_hook'] = 'pyramid_tm.explicit_manager'
    authn_policy = AuthTktAuthenticationPolicy(
        'sosecret', callback=groupfinder, hashalg='sha512')
    authz_policy = ACLAuthorizationPolicy()
    with Configurator(settings=settings) as config:
        config.set_authentication_policy(authn_policy)
        config.set_authorization_policy(authz_policy)
        config.include('pyramid_chameleon')

Only the highlighted lines need to be added.

We are enabling an AuthTktAuthenticationPolicy, which is based in an auth ticket that may be included in the request. We are also enabling an ACLAuthorizationPolicy, which uses an ACL to determine the allow or deny outcome for a view.

Note that the pyramid.authentication.AuthTktAuthenticationPolicy constructor accepts two arguments: secret and callback. secret is a string representing an encryption key used by the "authentication ticket" machinery represented by this policy: it is required. The callback is the groupfinder() function that we created before.

Add permission declarations¶

Open tutorial/views.py and add a permission='edit' parameter to the @view_config decorators for add_page() and edit_page():

@view_config(name='add_page', context='.models.Wiki',
             renderer='templates/edit.pt',
             permission='edit')

@view_config(name='edit_page', context='.models.Page',
             renderer='templates/edit.pt',
             permission='edit')

Only the highlighted lines, along with their preceding commas, need to be edited and added.

The result is that only users who possess the edit permission at the time of the request may invoke those two views.

Add a permission='view' parameter to the @view_config decorator for view_wiki() and view_page() as follows:

@view_config(context='.models.Wiki',
             permission='view')

@view_config(context='.models.Page', renderer='templates/view.pt',
             permission='view')

Only the highlighted lines, along with their preceding commas, need to be edited and added.

This allows anyone to invoke these two views.

We are done with the changes needed to control access. The changes that follow will add the login and logout feature.

Login, logout¶

Add login and logout views¶

We'll add a login view which renders a login form and processes the post from the login form, checking credentials.

We'll also add a logout view callable to our application and provide a link to it. This view will clear the credentials of the logged in user and redirect back to the front page.

Add the following import statements to the head of tutorial/views.py:

from pyramid.view import (
    view_config,
    forbidden_view_config,
    )

from pyramid.security import (
    remember,
    forget,
    )


from .security import USERS, check_password

All the highlighted lines need to be added or edited.

forbidden_view_config() will be used to customize the default 403 Forbidden page. remember() and forget() help to create and expire an auth ticket cookie.

Now add the login and logout views at the end of the file:

@view_config(context='.models.Wiki', name='login',
             renderer='templates/login.pt')
@forbidden_view_config(renderer='templates/login.pt')
def login(request):
    login_url = request.resource_url(request.context, 'login')
    referrer = request.url
    if referrer == login_url:
        referrer = '/'  # never use the login form itself as came_from
    came_from = request.params.get('came_from', referrer)
    message = ''
    login = ''
    password = ''
    if 'form.submitted' in request.params:
        login = request.params['login']
        password = request.params['password']
        if check_password(USERS.get(login), password):
            headers = remember(request, login)
            return HTTPFound(location=came_from,
                             headers=headers)
        message = 'Failed login'

    return dict(
        message=message,
        url=request.application_url + '/login',
        came_from=came_from,
        login=login,
        password=password,
    )


@view_config(context='.models.Wiki', name='logout')
def logout(request):
    headers = forget(request)
    return HTTPFound(location=request.resource_url(request.context),
                     headers=headers)

login() has two decorators:

a @view_config decorator which associates it with the login route and makes it visible when we visit /login,
a @forbidden_view_config decorator which turns it into a forbidden view. login() will be invoked when a user tries to execute a view callable for which they lack authorization. For example, if a user has not logged in and tries to add or edit a Wiki page, they will be shown the login form before being allowed to continue.

The order of these two view configuration decorators is unimportant.

logout() is decorated with a @view_config decorator which associates it with the logout route. It will be invoked when we visit /logout.

Add the `login.pt` Template¶

Create tutorial/templates/login.pt with the following content:

<!DOCTYPE html>
<html lang="${request.locale_name}">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="pyramid web application">
    <meta name="author" content="Pylons Project">
    <link rel="shortcut icon" href="${request.static_url('tutorial:static/pyramid-16x16.png')}">

    <title>Login - Pyramid tutorial wiki (based on
    TurboGears 20-Minute Wiki)</title>

    <!-- Bootstrap core CSS -->
    <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">

    <!-- Custom styles for this scaffold -->
    <link href="${request.static_url('tutorial:static/theme.css')}" rel="stylesheet">

    <!-- HTML5 shiv and Respond.js IE8 support of HTML5 elements and media queries -->
    <!--[if lt IE 9]>
      <script src="//oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js" integrity="sha384-0s5Pv64cNZJieYFkXYOTId2HMA2Lfb6q2nAcx2n0RTLUnCAoTTsS0nKEO27XyKcY" crossorigin="anonymous"></script>
      <script src="//oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js" integrity="sha384-ZoaMbDF+4LeFxg6WdScQ9nnR1QC2MIRxA1O9KWEXQwns1G8UNyIEZIQidzb0T1fo" crossorigin="anonymous"></script>
    <![endif]-->
  </head>

  <body>

    <div class="starter-template">
      <div class="container">
        <div class="row">
          <div class="col-md-2">
            <img class="logo img-responsive" src="${request.static_url('tutorial:static/pyramid.png')}" alt="pyramid web framework">
          </div>
          <div class="col-md-10">
            <div class="content">
              <p>
                <strong>
                  Login
                </strong><br>
                <span tal:replace="message"></span>
              </p>
              <form action="${url}" method="post">
                <input type="hidden" name="came_from" value="${came_from}">
                <div class="form-group">
                  <label for="login">Username</label>
                  <input type="text" name="login" value="${login}">
                </div>
                <div class="form-group">
                  <label for="password">Password</label>
                  <input type="password" name="password" value="${password}">
                </div>
                <div class="form-group">
                  <button type="submit" name="form.submitted" value="Log In" class="btn btn-default">Log In</button>
                </div>
              </form>
            </div>
          </div>
        </div>
        <div class="row">
          <div class="copyright">
            Copyright &copy; Pylons Project
          </div>
        </div>
      </div>
    </div>


    <!-- Bootstrap core JavaScript
    ================================================== -->
    <!-- Placed at the end of the document so the pages load faster -->
    <script src="//code.jquery.com/jquery-1.12.4.min.js" integrity="sha256-ZosEbRLbNQzLpnKIkEdrPv7lOy9C27hHQ+Xp8a4MxAQ=" crossorigin="anonymous"></script>
    <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
  </body>
</html>

The above template is referenced in the login view that we just added in views.py.

Return a `logged_in` flag to the renderer¶

Open tutorial/views.py again. Add a logged_in parameter to the return value of view_page(), add_page(), and edit_page() as follows:

    return dict(page=context, content=content, edit_url=edit_url,
                logged_in=request.authenticated_userid)

    return dict(page=page, save_url=save_url,
                logged_in=request.authenticated_userid)

    return dict(page=context,
                save_url=request.resource_url(context, 'edit_page'),
                logged_in=request.authenticated_userid)