auth/auth_tkt.py: enable overriding digest algorithms

Currently, mod_auth_tkt supports also SHA256 and SHA 512 [1],
not just plain MD5.  Quoting:

----v----
The default is MD5, which is faster, but has now been shown to be
vulnerable to collision attacks. Such attacks are not directly applicable
to mod_auth_tkt, which primarily relies on the security of the shared
secret rather than the strength of the hashing scheme. More paranoid users
will probably prefer to use one of the SHA digest types, however.

The default is likely to change in a future version, so setting the digest
type explicitly is encouraged.
----^----

Thus, enable it also in this implementation so one can optionally switch
to a stronger secure hash.

Backward compatibility should be untouched as ``md5`` is being passed
as a default kwarg.  The only change affecting external world is
a new parameter required at ``calculate_digest`` (specifying the
digest to use), but as it has probably no use outside the module,
this is a non-issue.  Alternatively: another optional kwarg.


Update (based Ian's comments):
The algorithm can also be specified as a string referring to the
algorithm known to hashlib (otherwise AttributeError will be raised).


Example session I used to check it works as expected (longish):

>>> import sys; sys.path.append('../..')
>>> from hashlib import sha256, sha512
>>> execfile('auth_tkt.py')
>>> AuthTicket('secret', 'me', '0.0.0.0').cookie_value()
'39fecb1395af5285232be390eba0eed34f5518c8me!'
>>> AuthTicket('secret', 'me', '0.0.0.0', "md5").cookie_value()
'c3b8eacbbbf76a9c993c7dcb99975d504f5518cfme!m,d,5!'
>>> AuthTicket('secret', 'me', '0.0.0.0', digest_algo="md5") \
... .cookie_value()
'db3b04de3c44b5bd0e2b47019e903c064f5518dbme!'
>>> AuthTicket('secret', 'me', '0.0.0.0', digest_algo="sha1") \
... .cookie_value()
'dddaadc2be960b6e89263ae7fb8c39591554103d4f5518edme!'
>>> AuthTicket('secret', 'me', '0.0.0.0', digest_algo=sha256) \
... .cookie_value()
'bf5c9a32e49920f2ca517ec19a9d55e10a83849e5d532e8997891b8ccdbf0e634f551902me!'
>>> AuthTicket('secret', 'me', '0.0.0.0', digest_algo="sha256") \
... .cookie_value()
'9cb12df90fd86b868c98353115df4da3b8f9fa83bebecdf0b7918fea5d06b0744f551908me!'
>>> AuthTicket('secret', 'me', '0.0.0.0', digest_algo='foo') \
... .cookie_value()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "auth_tkt.py", line 107, in __init__
    self.digest_algo = getattr(hashlib, digest_algo)
AttributeError: 'module' object has no attribute 'foo'
>>>
>>> parse_ticket('secret', \
...     AuthTicket('secret', 'me', '0.0.0.0').cookie_value(),'0.0.0.0')
(1330977060, 'me', [''], '')
>>> parse_ticket('secret', \
...     AuthTicket('secret', 'me', '0.0.0.0', digest_algo='md5') \
... .cookie_value(),'0.0.0.0', digest_algo='md5')
(1330977096, 'me', [''], '')
>>> parse_ticket('secret', \
...     AuthTicket('secret', 'me', '0.0.0.0', digest_algo=sha256) \
... .cookie_value(),'0.0.0.0', digest_algo=sha256)
(1330977115, 'me', [''], '')
>>> parse_ticket('secret', \
...     AuthTicket('secret', 'me', '0.0.0.0', digest_algo=sha512) \
... .cookie_value(),'0.0.0.0', digest_algo=sha512)
(1330977125, 'me', [''], '')
>>> parse_ticket('secret', \
...     AuthTicket('secret', 'me', '0.0.0.0', digest_algo=sha512) \
... .cookie_value(),'0.0.0.0')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "auth_tkt.py", line 179, in parse_ticket
    expected=(expected, digest))
__main__.BadTicket: Digest signature is not correct


[1] http://linux.die.net/man/3/mod_auth_tkt

1 files changed, 22 insertions, 8 deletions

diff --git a/paste/auth/auth_tkt.py b/paste/auth/auth_tkt.py
index a20e498..f3240ee 100644
--- a/paste/auth/auth_tkt.py
+++ b/paste/auth/auth_tkt.py
@@ -39,15 +39,16 @@ non-Python code run under Apache.
 
 import time as time_mod
 try:
-    from hashlib import md5
+    import hashlib
 except ImportError:
-    from md5 import md5
+    # mimic hashlib (will work for md5, fail for secure hashes)
+    import md5 as hashlib
 import Cookie
 from paste import request
 from urllib import quote as url_quote
 from urllib import unquote as url_unquote
 
-DEFAULT_DIGEST = md5
+DEFAULT_DIGEST = hashlib.md5
 
 
 class AuthTicket(object):
@@ -58,7 +59,8 @@ class AuthTicket(object):
     can include tokens (a list of strings, representing role names),
     'user_data', which is arbitrary data available for your own use in
     later scripts.  Lastly, you can override the timestamp, cookie name,
-    whether to secure the cookie and the digest algorithm.
+    whether to secure the cookie and the digest algorithm (for details
+    look at ``AuthTKTMiddleware``).
 
     Once you provide all the arguments, use .cookie_value() to
     generate the appropriate authentication ticket.  .cookie()
@@ -100,7 +102,11 @@ class AuthTicket(object):
             self.time = time
         self.cookie_name = cookie_name
         self.secure = secure
-        self.digest_algo = digest_algo
+        if isinstance(digest_algo, str):
+            # correct specification of digest from hashlib or fail
+            self.digest_algo = getattr(hashlib, digest_algo)
+        else:
+            self.digest_algo = digest_algo
 
     def digest(self):
         return calculate_digest(
@@ -142,6 +148,9 @@ def parse_ticket(secret, ticket, ip, digest_algo=DEFAULT_DIGEST):
     If the ticket cannot be parsed, ``BadTicket`` will be raised with
     an explanation.
     """
+    if isinstance(digest_algo, str):
+        # correct specification of digest from hashlib or fail
+        digest_algo = getattr(hashlib, digest_algo)
     digest_hexa_size = digest_algo().digest_size * 2
     ticket = ticket.strip('"')
     digest = ticket[:digest_hexa_size]
@@ -174,6 +183,7 @@ def parse_ticket(secret, ticket, ip, digest_algo=DEFAULT_DIGEST):
     return (timestamp, userid, tokens, user_data)
 
 
+# @@: Digest object constructor compatible with named ones in hashlib only
 def calculate_digest(ip, timestamp, secret, userid, tokens, user_data,
                      digest_algo):
     secret = maybe_encode(secret)
@@ -241,8 +251,8 @@ class AuthTKTMiddleware(object):
         when they visit this page.
 
     ``digest_algo``:
-        Digest object constructor compatible with named constructors from
-        ``hashlib``.
+        Digest algorithm specified as a name of the algorithm provided by
+        ``hashlib`` or as a compatible digest object constructor.
         Defaults to ``md5``, as in mod_auth_tkt.  The others currently
         compatible with mod_auth_tkt are ``sha256`` and ``sha512``.
 
@@ -276,7 +286,11 @@ class AuthTKTMiddleware(object):
         self.no_domain_cookie = no_domain_cookie
         self.current_domain_cookie = current_domain_cookie
         self.wildcard_cookie = wildcard_cookie
-        self.digest_algo = digest_algo
+        if isinstance(digest_algo, str):
+            # correct specification of digest from hashlib or fail
+            self.digest_algo = getattr(hashlib, digest_algo)
+        else:
+            self.digest_algo = digest_algo
 
     def __call__(self, environ, start_response):
         cookies = request.get_cookies(environ)