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Filename : wrapper.py
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# -*- test-case-name: twisted.web.test.test_httpauth -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
A guard implementation which supports HTTP header-based authentication
schemes.

If no I{Authorization} header is supplied, an anonymous login will be
attempted by using a L{Anonymous} credentials object.  If such a header is
supplied and does not contain allowed credentials, or if anonymous login is
denied, a 401 will be sent in the response along with I{WWW-Authenticate}
headers for each of the allowed authentication schemes.
"""

from __future__ import absolute_import, division

from twisted.cred import error
from twisted.cred.credentials import Anonymous
from twisted.python.compat import unicode
from twisted.python.components import proxyForInterface
from twisted.web import util
from twisted.web.resource import ErrorPage, IResource
from twisted.logger import Logger

from zope.interface import implementer


@implementer(IResource)
class UnauthorizedResource(object):
    """
    Simple IResource to escape Resource dispatch
    """
    isLeaf = True


    def __init__(self, factories):
        self._credentialFactories = factories


    def render(self, request):
        """
        Send www-authenticate headers to the client
        """
        def ensureBytes(s):
            return s.encode('ascii') if isinstance(s, unicode) else s

        def generateWWWAuthenticate(scheme, challenge):
            l = []
            for k, v in challenge.items():
                k = ensureBytes(k)
                v = ensureBytes(v)
                l.append(k + b"=" + quoteString(v))
            return b" ".join([scheme, b", ".join(l)])

        def quoteString(s):
            return b'"' + s.replace(b'\\', b'\\\\').replace(b'"', b'\\"') + b'"'

        request.setResponseCode(401)
        for fact in self._credentialFactories:
            challenge = fact.getChallenge(request)
            request.responseHeaders.addRawHeader(
                b'www-authenticate',
                generateWWWAuthenticate(fact.scheme, challenge))
        if request.method == b'HEAD':
            return b''
        return b'Unauthorized'


    def getChildWithDefault(self, path, request):
        """
        Disable resource dispatch
        """
        return self



@implementer(IResource)
class HTTPAuthSessionWrapper(object):
    """
    Wrap a portal, enforcing supported header-based authentication schemes.

    @ivar _portal: The L{Portal} which will be used to retrieve L{IResource}
        avatars.

    @ivar _credentialFactories: A list of L{ICredentialFactory} providers which
        will be used to decode I{Authorization} headers into L{ICredentials}
        providers.
    """
    isLeaf = False
    _log = Logger()

    def __init__(self, portal, credentialFactories):
        """
        Initialize a session wrapper

        @type portal: C{Portal}
        @param portal: The portal that will authenticate the remote client

        @type credentialFactories: C{Iterable}
        @param credentialFactories: The portal that will authenticate the
            remote client based on one submitted C{ICredentialFactory}
        """
        self._portal = portal
        self._credentialFactories = credentialFactories


    def _authorizedResource(self, request):
        """
        Get the L{IResource} which the given request is authorized to receive.
        If the proper authorization headers are present, the resource will be
        requested from the portal.  If not, an anonymous login attempt will be
        made.
        """
        authheader = request.getHeader(b'authorization')
        if not authheader:
            return util.DeferredResource(self._login(Anonymous()))

        factory, respString = self._selectParseHeader(authheader)
        if factory is None:
            return UnauthorizedResource(self._credentialFactories)
        try:
            credentials = factory.decode(respString, request)
        except error.LoginFailed:
            return UnauthorizedResource(self._credentialFactories)
        except:
            self._log.failure("Unexpected failure from credentials factory")
            return ErrorPage(500, None, None)
        else:
            return util.DeferredResource(self._login(credentials))


    def render(self, request):
        """
        Find the L{IResource} avatar suitable for the given request, if
        possible, and render it.  Otherwise, perhaps render an error page
        requiring authorization or describing an internal server failure.
        """
        return self._authorizedResource(request).render(request)


    def getChildWithDefault(self, path, request):
        """
        Inspect the Authorization HTTP header, and return a deferred which,
        when fired after successful authentication, will return an authorized
        C{Avatar}. On authentication failure, an C{UnauthorizedResource} will
        be returned, essentially halting further dispatch on the wrapped
        resource and all children
        """
        # Don't consume any segments of the request - this class should be
        # transparent!
        request.postpath.insert(0, request.prepath.pop())
        return self._authorizedResource(request)


    def _login(self, credentials):
        """
        Get the L{IResource} avatar for the given credentials.

        @return: A L{Deferred} which will be called back with an L{IResource}
            avatar or which will errback if authentication fails.
        """
        d = self._portal.login(credentials, None, IResource)
        d.addCallbacks(self._loginSucceeded, self._loginFailed)
        return d


    def _loginSucceeded(self, args):
        """
        Handle login success by wrapping the resulting L{IResource} avatar
        so that the C{logout} callback will be invoked when rendering is
        complete.
        """
        interface, avatar, logout = args
        class ResourceWrapper(proxyForInterface(IResource, 'resource')):
            """
            Wrap an L{IResource} so that whenever it or a child of it
            completes rendering, the cred logout hook will be invoked.

            An assumption is made here that exactly one L{IResource} from
            among C{avatar} and all of its children will be rendered.  If
            more than one is rendered, C{logout} will be invoked multiple
            times and probably earlier than desired.
            """
            def getChildWithDefault(self, name, request):
                """
                Pass through the lookup to the wrapped resource, wrapping
                the result in L{ResourceWrapper} to ensure C{logout} is
                called when rendering of the child is complete.
                """
                return ResourceWrapper(self.resource.getChildWithDefault(name, request))

            def render(self, request):
                """
                Hook into response generation so that when rendering has
                finished completely (with or without error), C{logout} is
                called.
                """
                request.notifyFinish().addBoth(lambda ign: logout())
                return super(ResourceWrapper, self).render(request)

        return ResourceWrapper(avatar)


    def _loginFailed(self, result):
        """
        Handle login failure by presenting either another challenge (for
        expected authentication/authorization-related failures) or a server
        error page (for anything else).
        """
        if result.check(error.Unauthorized, error.LoginFailed):
            return UnauthorizedResource(self._credentialFactories)
        else:
            self._log.failure(
                "HTTPAuthSessionWrapper.getChildWithDefault encountered "
                "unexpected error",
                failure=result,
            )
            return ErrorPage(500, None, None)


    def _selectParseHeader(self, header):
        """
        Choose an C{ICredentialFactory} from C{_credentialFactories}
        suitable to use to decode the given I{Authenticate} header.

        @return: A two-tuple of a factory and the remaining portion of the
            header value to be decoded or a two-tuple of L{None} if no
            factory can decode the header value.
        """
        elements = header.split(b' ')
        scheme = elements[0].lower()
        for fact in self._credentialFactories:
            if fact.scheme == scheme:
                return (fact, b' '.join(elements[1:]))
        return (None, None)