The example python code in customizing.html under the 
heading "Using an external password validation source" has a 
couple of bugs.

First, the script needs to import the os and crypt modules. I 
added the following as the first line of the script:

import os, crypt

 Second, the line

                return crypt.crypt(password, ent[1][:2]) == ent[1]

should be 

                return crypt.crypt(password, ent[1]) == ent[1]

Finally, to match better with the following example on "Using a 
UN*X passwd file as the user database", it would be best to use 
the same file name in both examples. I changed

        file = os.path.join(self.db.config.TRACKER_HOME, 
'passwd.txt')

to

        file = os.path.join(self.db.config.TRACKER_HOME, 
'users.passwd')