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# (c) 2005 Clark C. Evans
# This module is part of the Python Paste Project and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
# This code was written with funding by http://prometheusresearch.com
"""
Cookie "Saved" Authentication
This authentication middleware saves the current REMOTE_USER,
REMOTE_SESSION, and any other environment variables specified in a
cookie so that it can be retrieved during the next request without
requiring re-authentication. This uses a session cookie on the client
side (so it goes away when the user closes their window) and does
server-side expiration.
Following is a very simple example where a form is presented asking for
a user name (no actual checking), and dummy session identifier (perhaps
corresponding to a database session id) is stored in the cookie.
::
>>> from paste.httpserver import serve
>>> from paste.fileapp import DataApp
>>> from paste.httpexceptions import *
>>> # from paste.auth.cookie import AuthCookiehandler
>>> from paste.wsgilib import parse_querystring
>>> def testapp(environ, start_response):
... user = dict(parse_querystring(environ)).get('user','')
... if user:
... environ['REMOTE_USER'] = user
... environ['REMOTE_SESSION'] = 'a-session-id'
... if environ.get('REMOTE_USER'):
... page = '<html><body>Welcome %s (%s)</body></html>'
... page %= (environ['REMOTE_USER'], environ['REMOTE_SESSION'])
... else:
... page = ('<html><body><form><input name="user" />'
... '<input type="submit" /></form></body></html>')
... return DataApp(page, content_type="text/html")(
... environ, start_response)
>>> serve(AuthCookieHandler(testapp))
serving on...
"""
import sha, hmac, base64, random, time, string, warnings
from paste.request import get_cookies
def make_time(value):
return time.strftime("%Y%m%d%H%M",time.gmtime(value))
_signature_size = len(hmac.new('x','x',sha).digest())
_header_size = _signature_size + len(make_time(time.time()))
# build encode/decode functions to safely pack away values
_encode = [('\\','\\x5c'),('"','\\x22'),('=','\\x3d'),(';','\\x3b')]
_decode = [(v,k) for (k,v) in _encode]
_decode.reverse()
def encode(s, sublist = _encode):
return reduce((lambda a,(b,c): string.replace(a,b,c)), sublist, str(s))
decode = lambda s: encode(s,_decode)
class CookieTooLarge(RuntimeError):
def __init__(self, content, cookie):
RuntimeError.__init__("Signed cookie exceeds maximum size of 4096")
self.content = content
self.cookie = cookie
_all_chars = ''.join([chr(x) for x in range(0,255)])
def new_secret():
""" returns a 64 byte secret """
return ''.join(random.sample(_all_chars,64))
class AuthCookieSigner:
"""
save/restore ``environ`` entries via digially signed cookie
This class converts content into a timed and digitally signed
cookie, as well as having the facility to reverse this procedure.
If the cookie, after the content is encoded and signed exceeds the
maximum length (4096), then CookieTooLarge exception is raised.
The timeout of the cookie is handled on the server side for a few
reasons. First, if a 'Expires' directive is added to a cookie, then
the cookie becomes persistent (lasting even after the browser window
has closed). Second, the user's clock may be wrong (perhaps
intentionally). The timeout is specified in minutes; and expiration
date returned is rounded to one second.
Constructor Arguments:
``secret``
This is a secret key if you want to syncronize your keys so
that the cookie will be good across a cluster of computers.
It is recommended via the HMAC specification (RFC 2104) that
the secret key be 64 bytes since this is the block size of
the hashing. If you do not provide a secret key, a random
one is generated each time you create the handler; this
should be sufficient for most cases.
``timeout``
This is the time (in minutes) from which the cookie is set
to expire. Note that on each request a new (replacement)
cookie is sent, hence this is effectively a session timeout
parameter for your entire cluster. If you do not provide a
timeout, it is set at 30 minutes.
``maxlen``
This is the maximum size of the *signed* cookie; hence the
actual content signed will be somewhat less. If the cookie
goes over this size, a ``CookieTooLarge`` exception is
raised so that unexpected handling of cookies on the client
side are avoided. By default this is set at 4k (4096 bytes),
which is the standard cookie size limit.
"""
def __init__(self, secret = None, timeout = None, maxlen = None):
self.timeout = timeout or 30
self.maxlen = maxlen or 4096
self.secret = secret or new_secret()
def sign(self, content):
"""
Sign the content returning a valid cookie (that does not
need to be escaped and quoted). The expiration of this
cookie is handled server-side in the auth() function.
"""
cookie = base64.b64encode(
hmac.new(self.secret,content,sha).digest() +
make_time(time.time()+60*self.timeout) +
content).replace("/","_").replace("=","~")
if len(cookie) > self.maxlen:
raise CookieTooLarge(content,cookie)
return cookie
def auth(self,cookie):
"""
Authenticate the cooke using the signature, verify that it
has not expired; and return the cookie's content
"""
decode = base64.b64decode(
cookie.replace("_","/").replace("~","="))
signature = decode[:_signature_size]
expires = decode[_signature_size:_header_size]
content = decode[_header_size:]
if signature == hmac.new(self.secret,content,sha).digest():
if int(expires) > int(make_time(time.time())):
return content
else:
# This is the normal case of an expired cookie; just
# don't bother doing anything here.
pass
else:
# This case can happen if the server is restarted with a
# different secret; or if the user's IP address changed
# due to a proxy. However, it could also be a break-in
# attempt -- so should it be reported?
pass
class AuthCookieEnviron(list):
"""
a list of environment keys to be saved via cookie
An instance of this object, found at ``environ['paste.auth.cookie']``
lists the `environ` keys that were restored from or will be added
to the digially signed cookie. This object can be accessed from an
`environ` variable by using this module's name.
"""
def __init__(self, handler, scanlist):
list.__init__(self, scanlist)
self.handler = handler
def append(self, value):
if value in self:
return
list.append(self,str(value))
class AuthCookieHandler:
"""
the actual handler that should be put in your middleware stack
This middleware uses cookies to stash-away a previously authenticated
user (and perhaps other variables) so that re-authentication is not
needed. This does not implement sessions; and therefore N servers
can be syncronized to accept the same saved authentication if they
all use the same cookie_name and secret.
By default, this handler scans the `environ` for the REMOTE_USER
key; if found, it is stored. It can be configured to scan other
`environ` keys as well -- but be careful not to exceed 2-3k (so that
the encoded and signed cookie does not exceed 4k). You can ask it
to handle other environment variables by doing:
``environ['paste.auth.cookie'].append('your.environ.variable')``
Constructor Arguments:
``application``
This is the wrapped application which will have access to
the ``environ['REMOTE_USER']`` restored by this middleware.
``cookie_name``
The name of the cookie used to store this content, by default
it is ``PASTE_AUTH_COOKIE``.
``scanlist``
This is the initial set of ``environ`` keys to save/restore
to the signed cookie. By default is consists only of
``REMOTE_USER``; any tuple or list of environment keys
will work. However, be careful, as the total saved size is
limited to around 3k.
``signer``
This is the signer object used to create the actual cookie
values, by default, it is ``AuthCookieSigner`` and is passed
the remaining arguments to this function: ``secret``,
``timeout``, and ``maxlen``.
At this time, each cookie is individually signed. To store more
than the 4k of data; it is possible to sub-class this object to
provide different ``environ_name`` and ``cookie_name``
"""
environ_name = 'paste.auth.cookie'
cookie_name = 'PASTE_AUTH_COOKIE'
signer_class = AuthCookieSigner
environ_class = AuthCookieEnviron
def __init__(self, application, cookie_name=None, scanlist=None,
signer=None, secret=None, timeout=None, maxlen=None):
if not signer:
signer = self.signer_class(secret,timeout,maxlen)
self.signer = signer
self.scanlist = scanlist or ('REMOTE_USER','REMOTE_SESSION')
self.application = application
self.cookie_name = cookie_name or self.cookie_name
def __call__(self, environ, start_response):
if self.environ_name in environ:
raise AssertionError("AuthCookie already installed!")
scanlist = self.environ_class(self,self.scanlist)
jar = get_cookies(environ)
if jar.has_key(self.cookie_name):
content = self.signer.auth(jar[self.cookie_name].value)
if content:
for pair in content.split(";"):
(k,v) = pair.split("=")
k = decode(k)
if k not in scanlist:
scanlist.append(k)
if k in environ:
continue
environ[k] = decode(v)
if 'REMOTE_USER' == k:
environ['AUTH_TYPE'] = 'cookie'
environ[self.environ_name] = scanlist
if "paste.httpexceptions" in environ:
warnings.warn("Since paste.httpexceptions is hooked in your "
"processing chain before paste.auth.cookie, if an "
"HTTPRedirection is raised, the cookies this module sets "
"will not be included in your response.\n")
def response_hook(status, response_headers, exc_info=None):
"""
Scan the environment for keys specified in the scanlist,
pack up their values, signs the content and issues a cookie.
"""
scanlist = environ.get(self.environ_name)
assert scanlist and isinstance(scanlist,self.environ_class)
content = []
for k in scanlist:
v = environ.get(k,None)
if v is not None:
content.append("%s=%s" % (encode(k),encode(v)))
if content:
content = ";".join(content)
content = self.signer.sign(content)
cookie = '%s=%s; Path=/;' % (self.cookie_name, content)
if 'https' == environ['wsgi.url_scheme']:
cookie += ' secure;'
response_headers.append(('Set-Cookie',cookie))
return start_response(status, response_headers, exc_info)
return self.application(environ, response_hook)
middleware = AuthCookieHandler
__all__ = ['AuthCookieHandler', 'AuthCookieSigner', 'AuthCookieEnviron']
if "__main__" == __name__:
import doctest
doctest.testmod(optionflags=doctest.ELLIPSIS)
|
