path: root/repoze/bfg/security.py

import logging
import os
import sys

from zope.interface import implements
from zope.component import queryUtility

from zope.location.location import LocationIterator

from repoze.bfg.interfaces import ISecurityPolicy
from repoze.bfg.interfaces import IViewPermission
from repoze.bfg.interfaces import IViewPermissionFactory
from repoze.bfg.interfaces import NoAuthorizationInformation

Everyone = 'system.Everyone'
Authenticated = 'system.Authenticated'
Allow = 'Allow'
Deny = 'Deny'

def has_permission(permission, context, request):
    """ Provided a permission (a string or unicode object), a context
    (a model instance) and a request object, return an instance of
    ``Allowed`` if the permission is granted in this context to the
    user implied by the request. Return an instance of ``Denied`` if
    this permission is not granted in this context to this user.  This
    delegates to the current security policy.  Return True
    unconditionally if no security policy has been configured in this
    application."""
    policy = queryUtility(ISecurityPolicy)
    if policy is None:
        return True
    return policy.permits(context, request, permission)

def authenticated_userid(request):
    """ Return the userid of the currently authenticated user or
    ``None`` if there is no security policy in effect or there is no
    currently authenticated user"""
    policy = queryUtility(ISecurityPolicy)
    if policy is None:
        return None
    return policy.authenticated_userid(request)

def effective_principals(request):
    """ Return the list of 'effective' principal identifiers for the
    request.  This will include the userid of the currently
    authenticated user if a user is currently authenticated. If no
    security policy is in effect, this will return an empty sequence."""
    policy = queryUtility(ISecurityPolicy)
    if policy is None:
        return []
    return policy.effective_principals(request)

def principals_allowed_by_permission(context, permission):
    """ Provided a context (a model object), and a permission (a
    string or unicode object), return a sequence of principal ids that
    possess the permission in the context.  If no security policy is
    in effect, this will return a sequence with the single value
    representing ``Everyone`` (the special principal identifier
    representing all principals).  Note that even if a security policy
    *is* in effect, some security policies may not implement the
    required machinery for this function; those will cause a
    ``NotImplementedError`` exception to be raised when this function
    is invoked."""
    policy = queryUtility(ISecurityPolicy)
    if policy is None:
        return [Everyone]
    return policy.principals_allowed_by_permission(context, permission)

class ACLAuthorizer(object):

    def __init__(self, context, logger=None):
        self.context = context
        self.logger = logger

    def permits(self, permission, *principals):
        acl = getattr(self.context, '__acl__', None)
        if acl is None:
            raise NoAuthorizationInformation('%s item has no __acl__' % acl)

        for ace in acl:
            ace_action, ace_principal, ace_permissions = ace
            for principal in flatten(principals):
                if ace_principal == principal:
                    permissions = flatten(ace_permissions)
                    if permission in permissions:
                        action = ace_action
                        if action == Allow:
                            result = Allowed(ace, acl, permission, principals,
                                             self.context)
                            self.logger and self.logger.debug(str(result))
                            return result
                        result = Denied(ace, acl, permission, principals,
                                        self.context)
                        self.logger and self.logger.debug(str(result))
                        return result
        result = Denied(None, acl, permission, principals, self.context)
        self.logger and self.logger.debug(str(result))
        return result

class ACLSecurityPolicy(object):
    implements(ISecurityPolicy)
    authorizer_factory = ACLAuthorizer
    
    def __init__(self, logger, get_principals):
        self.logger = logger
        self.get_principals = get_principals

    def permits(self, context, request, permission):
        """ Return ``Allowed`` if the policy permits access,
        ``Denied`` if not."""
        principals = self.effective_principals(request)
        for location in LocationIterator(context):
            authorizer = self.authorizer_factory(location, self.logger)
            try:
                return authorizer.permits(permission, *principals)
            except NoAuthorizationInformation:
                continue

        return False

    def authenticated_userid(self, request):
        principals = self.get_principals(request)
        if principals:
            return principals[0]

    def effective_principals(self, request):
        effective_principals = [Everyone]
        principal_ids = self.get_principals(request)

        if principal_ids:
            effective_principals.append(Authenticated)
            effective_principals.extend(principal_ids)

        return effective_principals

    def principals_allowed_by_permission(self, context, permission):
        for location in LocationIterator(context):
            acl = getattr(location, '__acl__', None)
            if acl is not None:
                allowed = {}
                for ace in acl:
                    ace_action, ace_principal, ace_permissions = ace
                    if ace_action == Allow:
                        ace_permissions = flatten(ace_permissions)
                        for ace_permission in ace_permissions:
                            if ace_permission == permission:
                                allowed[ace_principal] = True
                return sorted(allowed.keys())
        return []

DEBUG_LOG_KEY = 'BFG_SECURITY_DEBUG'

def debug_logger(logger):
    if logger is None:
        do_debug_log = os.environ.get(DEBUG_LOG_KEY, '')
        if str(do_debug_log).lower() in ('1', 'y', 'true', 't', 'on'):
            handler = logging.StreamHandler(sys.stdout)
            fmt = '%(asctime)s %(message)s'
            formatter = logging.Formatter(fmt)
            handler.setFormatter(formatter)
            logger = logging.Logger('repoze.bfg.security')
            logger.addHandler(handler)
            logger.setLevel(logging.DEBUG)
            return logger
    return logger

def get_remoteuser(request):
    user_id = request.environ.get('REMOTE_USER')
    if user_id:
        return [user_id]
    return []

def RemoteUserACLSecurityPolicy(logger=None):
    """ A security policy which:

    - examines the request.environ for the REMOTE_USER variable and
      uses any non-false value as a principal id for this request.

    - uses an ACL-based authorization model which attempts to find an
      ACL on the context, and which returns ``Allowed`` from its
      'permits' method if the ACL found grants access to the current
      principal.  It returns ``Denied`` if permission was not granted
      (either explicitly via a deny or implicitly by not finding a
      matching ACE action).  An ACL is an ordered sequence of ACE
      tuples, e.g.  ``[(Allow, Everyone, 'read'), (Deny, 'george',
      'write')]``.  ACLs stored on model instance objects as their
      __acl__ attribute will be used by the security machinery to
      grant or deny access.

    """
    logger = debug_logger(logger)
    return ACLSecurityPolicy(logger, get_remoteuser)

def get_who_principals(request):
    identity = request.environ.get('repoze.who.identity')
    if not identity:
        return []
    principals = [identity['repoze.who.userid']]
    principals.extend(identity.get('groups', []))
    return principals

def RepozeWhoIdentityACLSecurityPolicy(logger=None):
    """ A security policy which:

    - examines the request.environ for the ``repoze.who.identity``
      dictionary.  If one is found, the principal ids for the request
      are composed of ``repoze.who.identity['repoze.who.userid']``
      plus ``repoze.who.identity.get('groups', []).

    - uses an ACL-based authorization model which attempts to find an
      ACL on the context, and which returns ``Allowed`` from its
      'permits' method if the ACL found grants access to the current
      principal.  It returns ``Denied`` if permission was not granted
      (either explicitly via a deny or implicitly by not finding a
      matching ACE action).  An ACL is an ordered sequence of ACE
      tuples, e.g.  ``[(Allow, Everyone, 'read'), (Deny, 'george',
      'write')]``.  ACLs stored on model instance objects as their
      __acl__ attribute will be used by the security machinery to
      grant or deny access.

    """
    logger = debug_logger(logger)
    return ACLSecurityPolicy(logger, get_who_principals)

class PermitsResult:
    def __init__(self, ace, acl, permission, principals, context):
        self.acl = acl
        self.ace = ace
        self.permission = permission
        self.principals = principals
        self.context_repr = repr(context)

    def __str__(self):
        msg = '%s: %r via ace %r in acl %r or principals %r in context %s'
        msg = msg % (self.__class__.__name__,
                     self.permission, self.ace, self.acl, self.principals,
                     self.context_repr)
        return msg

class Denied(PermitsResult):
    """ An instance of ``Denied`` is returned by an ACL denial.  It
    evaluates equal to all boolean false types.  It also has
    attributes which indicate which acl, ace, permission, principals,
    and context were involved in the request.  Its __str__ method
    prints a summary of these attributes for debugging purposes."""
    def __nonzero__(self):
        return False

    def __eq__(self, other):
        return bool(other) is False

class Allowed(PermitsResult):
    """ An instance of ``Allowed`` is returned by an ACL allow.  It
    evaluates equal to all boolean true types.  It also has attributes
    which indicate which acl, ace, permission, principals, and context
    were involved in the request.  Its __str__ method prints a summary
    of these attributes for debugging purposes."""
    def __nonzero__(self):
        return True

    def __eq__(self, other):
        return bool(other) is True

def flatten(x):
    """flatten(sequence) -> list

    Returns a single, flat list which contains all elements retrieved
    from the sequence and all recursively contained sub-sequences
    (iterables).

    Examples:
    >>> [1, 2, [3,4], (5,6)]
    [1, 2, [3, 4], (5, 6)]
    >>> flatten([[[1,2,3], (42,None)], [4,5], [6], 7, MyVector(8,9,10)])
    [1, 2, 3, 42, None, 4, 5, 6, 7, 8, 9, 10]"""
    if isinstance(x, basestring):
        return [x]
    result = []
    for el in x:
        if hasattr(el, "__iter__") and not isinstance(el, basestring):
            result.extend(flatten(el))
        else:
            result.append(el)
    return result

class ViewPermission(object):
    implements(IViewPermission)
    def __init__(self, context, request, permission_name):
        self.context = context
        self.request = request
        self.permission_name = permission_name
    
    def __call__(self, security_policy):
        return security_policy.permits(self.context, self.request,
                                       self.permission_name)

    def __repr__(self):
        return '<Permission at %s named %r for %r>' % (id(self),
                                                       self.permission_name,
                                                       self.request.view_name)
        
class ViewPermissionFactory(object):
    implements(IViewPermissionFactory)
    def __init__(self, permission_name):
        self.permission_name = permission_name

    def __call__(self, context, request):
        return ViewPermission(context, request, self.permission_name)

class Unauthorized(Exception):
    def __init__(self, message='Unauthorized'):
        self.message = message

    def __str__(self):
        return str(self.message)