# -*- coding: utf-8 -*-
"""
flask_principal
~~~~~~~~~~~~~~~
Identity management for Flask.
:copyright: (c) 2012 by Ali Afshar.
:license: MIT, see LICENSE for more details.
"""
from __future__ import with_statement
__version__ = '0.4.0'
import sys
from functools import partial, wraps
from collections import deque
from collections import namedtuple
from flask import g, session, current_app, abort, request
from flask.signals import Namespace
PY3 = sys.version_info[0] == 3
signals = Namespace()
identity_changed = signals.signal('identity-changed', doc="""
Signal sent when the identity for a request has been changed.
Actual name: ``identity-changed``
Authentication providers should send this signal when authentication has been
successfully performed. Flask-Principal connects to this signal and
causes the identity to be saved in the session.
For example::
from flaskext.principal import Identity, identity_changed
def login_view(req):
username = req.form.get('username')
# check the credentials
identity_changed.send(app, identity=Identity(username))
""")
identity_loaded = signals.signal('identity-loaded', doc="""
Signal sent when the identity has been initialised for a request.
Actual name: ``identity-loaded``
Identity information providers should connect to this signal to perform two
major activities:
1. Populate the identity object with the necessary authorization provisions.
2. Load any additional user information.
For example::
from flaskext.principal import identity_loaded, RoleNeed, UserNeed
@identity_loaded.connect
def on_identity_loaded(sender, identity):
# Get the user information from the db
user = db.get(identity.name)
# Update the roles that a user can provide
for role in user.roles:
identity.provides.add(RoleNeed(role.name))
# Save the user somewhere so we only look it up once
identity.user = user
""")
Need = namedtuple('Need', ['method', 'value'])
"""A required need
This is just a named tuple, and practically any tuple will do.
The ``method`` attribute can be used to look up element 0, and the ``value``
attribute can be used to look up element 1.
"""
UserNeed = partial(Need, 'id')
UserNeed.__doc__ = """A need with the method preset to `"id"`."""
RoleNeed = partial(Need, 'role')
RoleNeed.__doc__ = """A need with the method preset to `"role"`."""
TypeNeed = partial(Need, 'type')
TypeNeed.__doc__ = """A need with the method preset to `"type"`."""
ActionNeed = partial(Need, 'action')
TypeNeed.__doc__ = """A need with the method preset to `"action"`."""
ItemNeed = namedtuple('ItemNeed', ['method', 'value', 'type'])
"""A required item need
An item need is just a named tuple, and practically any tuple will do. In
addition to other Needs, there is a type, for example this could be specified
as::
ItemNeed('update', 27, 'posts')
('update', 27, 'posts') # or like this
And that might describe the permission to update a particular blog post. In
reality, the developer is free to choose whatever convention the permissions
are.
"""
class PermissionDenied(RuntimeError):
"""Permission denied to the resource"""
class Identity(object):
"""Represent the user's identity.
:param id: The user id
:param auth_type: The authentication type used to confirm the user's
identity.
The identity is used to represent the user's identity in the system. This
object is created on login, or on the start of the request as loaded from
the user's session.
Once loaded it is sent using the `identity-loaded` signal, and should be
populated with additional required information.
Needs that are provided by this identity should be added to the `provides`
set after loading.
"""
def __init__(self, id, auth_type=None):
self.id = id
self.auth_type = auth_type
self.provides = set()
def can(self, permission):
"""Whether the identity has access to the permission.
:param permission: The permission to test provision for.
"""
return permission.allows(self)
def __repr__(self):
return '<{0} id="{1}" auth_type="{2}" provides={3}>'.format(
self.__class__.__name__, self.id, self.auth_type, self.provides
)
class AnonymousIdentity(Identity):
"""An anonymous identity"""
def __init__(self):
Identity.__init__(self, None)
class IdentityContext(object):
"""The context of an identity for a permission.
.. note:: The principal is usually created by the flaskext.Permission.require method
call for normal use-cases.
The principal behaves as either a context manager or a decorator. The
permission is checked for provision in the identity, and if available the
flow is continued (context manager) or the function is executed (decorator).
"""
def __init__(self, permission, http_exception=None):
self.permission = permission
self.http_exception = http_exception
"""The permission of this principal
"""
@property
def identity(self):
"""The identity of this principal
"""
return g.identity
def can(self):
"""Whether the identity has access to the permission
"""
return self.identity.can(self.permission)
def __call__(self, f):
@wraps(f)
def _decorated(*args, **kw):
with self:
rv = f(*args, **kw)
return rv
return _decorated
def __enter__(self):
# check the permission here
if not self.can():
if self.http_exception:
abort(self.http_exception, self.permission)
raise PermissionDenied(self.permission)
def __exit__(self, *args):
return False
class Permission(object):
"""Represents needs, any of which must be present to access a resource
:param needs: The needs for this permission
"""
def __init__(self, *needs):
"""A set of needs, any of which must be present in an identity to have
access.
"""
self.needs = set(needs)
self.excludes = set()
def _bool(self):
return bool(self.can())
def __nonzero__(self):
"""Equivalent to ``self.can()``.
"""
return self._bool()
def __bool__(self):
"""Equivalent to ``self.can()``.
"""
return self._bool()
def __and__(self, other):
"""Does the same thing as ``self.union(other)``
"""
return self.union(other)
def __or__(self, other):
"""Does the same thing as ``self.difference(other)``
"""
return self.difference(other)
def __contains__(self, other):
"""Does the same thing as ``other.issubset(self)``.
"""
return other.issubset(self)
def __repr__(self):
return '<{0} needs={1} excludes={2}>'.format(
self.__class__.__name__, self.needs, self.excludes
)
def require(self, http_exception=None):
"""Create a principal for this permission.
The principal may be used as a context manager, or a decroator.
If ``http_exception`` is passed then ``abort()`` will be called
with the HTTP exception code. Otherwise a ``PermissionDenied``
exception will be raised if the identity does not meet the
requirements.
:param http_exception: the HTTP exception code (403, 401 etc)
"""
return IdentityContext(self, http_exception)
def test(self, http_exception=None):
"""
Checks if permission available and raises relevant exception
if not. This is useful if you just want to check permission
without wrapping everything in a require() block.
This is equivalent to::
with permission.require():
pass
"""
with self.require(http_exception):
pass
def reverse(self):
"""
Returns reverse of current state (needs->excludes, excludes->needs)
"""
p = Permission()
p.needs.update(self.excludes)
p.excludes.update(self.needs)
return p
def union(self, other):
"""Create a new permission with the requirements of the union of this
and other.
:param other: The other permission
"""
p = Permission(*self.needs.union(other.needs))
p.excludes.update(self.excludes.union(other.excludes))
return p
def difference(self, other):
"""Create a new permission consisting of requirements in this
permission and not in the other.
"""
p = Permission(*self.needs.difference(other.needs))
p.excludes.update(self.excludes.difference(other.excludes))
return p
def issubset(self, other):
"""Whether this permission needs are a subset of another
:param other: The other permission
"""
return (
self.needs.issubset(other.needs) and
self.excludes.issubset(other.excludes)
)
def allows(self, identity):
"""Whether the identity can access this permission.
:param identity: The identity
"""
if self.needs and not self.needs.intersection(identity.provides):
return False
if self.excludes and self.excludes.intersection(identity.provides):
return False
return True
def can(self):
"""Whether the required context for this permission has access
This creates an identity context and tests whether it can access this
permission
"""
return self.require().can()
class Denial(Permission):
"""
Shortcut class for passing excluded needs.
"""
def __init__(self, *excludes):
self.excludes = set(excludes)
self.needs = set()
def session_identity_loader():
if 'identity.id' in session and 'identity.auth_type' in session:
identity = Identity(session['identity.id'],
session['identity.auth_type'])
return identity
def session_identity_saver(identity):
session['identity.id'] = identity.id
session['identity.auth_type'] = identity.auth_type
session.modified = True
class Principal(object):
"""Principal extension
:param app: The flask application to extend
:param use_sessions: Whether to use sessions to extract and store
identification.
:param skip_static: Whether to ignore static endpoints.
"""
def __init__(self, app=None, use_sessions=True, skip_static=False):
self.identity_loaders = deque()
self.identity_savers = deque()
# XXX This will probably vanish for a better API
self.use_sessions = use_sessions
self.skip_static = skip_static
if app is not None:
self.init_app(app)
def _init_app(self, app):
from warnings import warn
warn(DeprecationWarning(
'_init_app is deprecated, use the new init_app '
'method instead.'), stacklevel=1
)
self.init_app(app)
def init_app(self, app):
if hasattr(app, 'static_url_path'):
self._static_path = app.static_url_path
else:
self._static_path = app.static_path
app.before_request(self._on_before_request)
identity_changed.connect(self._on_identity_changed, app)
if self.use_sessions:
self.identity_loader(session_identity_loader)
self.identity_saver(session_identity_saver)
def set_identity(self, identity):
"""Set the current identity.
:param identity: The identity to set
"""
self._set_thread_identity(identity)
for saver in self.identity_savers:
saver(identity)
def identity_loader(self, f):
"""Decorator to define a function as an identity loader.
An identity loader function is called before request to find any
provided identities. The first found identity is used to load from.
For example::
app = Flask(__name__)
principals = Principal(app)
@principals.identity_loader
def load_identity_from_weird_usecase():
return Identity('ali')
"""
self.identity_loaders.appendleft(f)
return f
def identity_saver(self, f):
"""Decorator to define a function as an identity saver.
An identity loader saver is called when the identity is set to persist
it for the next request.
For example::
app = Flask(__name__)
principals = Principal(app)
@principals.identity_saver
def save_identity_to_weird_usecase(identity):
my_special_cookie['identity'] = identity
"""
self.identity_savers.appendleft(f)
return f
def _set_thread_identity(self, identity):
g.identity = identity
identity_loaded.send(current_app._get_current_object(),
identity=identity)
def _on_identity_changed(self, app, identity):
if self._is_static_route():
return
self.set_identity(identity)
def _on_before_request(self):
if self._is_static_route():
return
g.identity = AnonymousIdentity()
for loader in self.identity_loaders:
identity = loader()
if identity is not None:
self.set_identity(identity)
return
def _is_static_route(self):
return (
self.skip_static and
request.path.startswith(self._static_path)
)
