Authenticate Via External Cookie

Requirements

The external cookie authentication alternative may be a good choice for your installation if your MoinMoin wiki topic is closely associated with some other application. You may be using MoinMoin for application documentation, popup help functions, or bug tracking. Several of your application pages may have hyperlinks to wiki pages. Wiki pages may contain custom macros that present data from your application database. Wiki users must login before they can update wiki pages (or you wish that were the case). Everyone with an application login ID also has a wiki login ID. Your users are annoyed that they frequently must login twice, first to the other application and then to MoinMoin. Your administrators are annoyed because they must maintain login IDs in two places.

To authenticate a MoinMoin user with an external cookie, your other application must be modified to create a cookie with each successful login. It must delete the cookie as part of the logout process.

In order to prevent hackers from easily creating their own cookie, MoinMoin transactions need to authenticate the cookie. One way to do this is to modify your other application to store a hash of the cookie value in a database, file, or other secure shared storage area that can be accessed by MoinMoin.

Strategy

The MoinMoin wiki code will be customized in two places. wikiconfig.py will be modified to create a new ExternalCookie class that will be used to authenticate a user. Logging in to your other application will effectively log you in to the wiki. Logging off of your other application will log you out of the wiki. Several variables will be added to wikiconfig.py to customize the Settings:Preferences page and to automatically create new user records when required.

Your wiki themes may be modified to override the username method of the Theme class. This method generates the login and logout hyperlinks within the wiki navigation area. These hyperlinks will be customized to point to the login and logout pages of your other application.

You must modify your other application as outlined above to create/delete a cookie and (optionally) add/delete entries to a shared storage area. If your wiki users can read the wiki without logging in, you may want to modify your other application login page so a wiki reader (logging in from a wiki page) will be returned to their referred-from page after login is complete (similar to the way MoinMoin login works).

Alternative Strategies Not Implemented

It is probably best to not synchronize inactivity timeouts between the other application and the wiki. If a logged in user on the other application times out after an hour of inactivity, he can continue to edit and save pages on the wiki provided the other application timeout process is not modified to delete the entry in the shared storage area. If the other application timed-out user logs in again, a new entry in the shared storage area will be created and a new MoinAuth cookie generated -- subsequent wiki transactions will use the new cookie. The example wikiconfig.py contains an example showing how inactive entries might be removed from a MySQL table soon after expiration by a MoinMoin transaction. However, most installations will probably choose to clear obsolete entries in the shared storage area with a process embedded in the other application.

One alternative to the use of a shared storage area is to encrypt the cookie in the other application and decrypt the cookie in the external_auth method. If this method were implemented, the addition of a timestamp to the cookie value could force cookies to timeout with the addition of an aging check. Without the aging check, any cookie generated would be valid forever (a minor issue) or until the encryption keys were changed. Brief tests with the ezPyCrypto example programs were discouraging because of the amount of compute time required. MySQL was faster -- the measured wall time to validate the cookie was usually 0 seconds and always less than 0.02 seconds.

Another possibility to thwart the use of stolen cookies is to add the authenticated user's IP address to the cookie value and then check it against the IP address of the incoming MoinMoin transaction. But this has marginal value because some ISPs (AOL) change the low order bits of the IP address with each transaction and in other cases several users could appear to be coming from the same IP address.

ExternalCookie Class

The first step is to override the external_auth method of the Config class by adding the code snippet below to your wikiconfig.py.

The code below is for Moin 1.9.

• edit your wikiconfig.py or farmconfig.py

• find the line containing class Config(DefaultConfig): or class FarmConfig(DefaultConfig):

• replace the above line with all of the code below

• if using farmconfig.py find and comment/uncomment the appropriate class statements

   1 
   2 
   3 
   4 
   5 
   6 
   7 
   8 
   9 
  10 
  11 
  12 
  13 from MoinMoin.config.multiconfig import DefaultConfig
  14 from MoinMoin.auth import BaseAuth
  15     
  16 
  17 import time
  18 def writeLog(*args): 
  19     '''Write an entry in a log file with a timestamp and all of the args.'''
  20     s = time.strftime('%Y-%m-%d %H:%M:%S ',time.localtime())
  21     for a in args:
  22         s = '%s %s;' % (s,a)
  23     log = open('/somelogfile', 'a') 
  24     log.write('\n' + s + '\n')
  25     log.close()
  26     return
  27     
  28 
  29 import MySQLdb
  30 def verifySession(sidHash): 
  31     """Return True if sidHash value exists (meaning user is currently logged on), false otherwise.  
  32     
  33     If you are not a MySQL user, find another way to store this information.  ActiveSession is a two-column table
  34     containing a hashed cookie value (sidHash) plus a date-time stamp (tStamp).
  35     Your other application must add an entry to this table each time a user logs on and delete the entry when the user logs off.
  36     """
  37     db = MySQLdb.connect(db='mydb',user='myid',passwd='mypw') 
  38     c = db.cursor()
  39     q = 'select sidHash from ActiveSession where sidHash="%s"' % sidHash
  40     result = c.execute(q)
  41     c.close()
  42     if result == 1:
  43         return True
  44     return False
  45     
  46 def verifySessionPlus(sidHash,timeout=3600*4): 
  47     """Return True if sidHash value exists (meaning user is currently logged on), false otherwise.  
  48     
  49     This version of verifySession deletes entries inactive for more than 4 hours and
  50     updates the tStamp field with each moin transaction.  If performance is 
  51     important, find another way to delete inactive sessions.
  52     """
  53     db = MySQLdb.connect(db='mydb',user='myid',passwd='mypw') 
  54     c = db.cursor()
  55     q = 'delete from ActiveSession where tStamp<"%s"' % int(time.time() - timeout) 
  56     result = c.execute(q)
  57     q = 'update ActiveSession set tStamp=%s where sidHash="%s"' % (int(time.time()),sidHash)
  58     result = c.execute(q)
  59     c.close()
  60     if result == 1:
  61         return True
  62     return False
  63     
  64 
  65 class ExternalCookie(BaseAuth):
  66     name = 'external_cookie'
  67     
  68     
  69     login_inputs = ['username', 'password'] 
  70     
  71     
  72     def __init__(self, autocreate=False):
  73         self.autocreate = autocreate
  74         BaseAuth.__init__(self)
  75 
  76     def request(self, request, user_obj, **kw):
  77         """Return (user-obj,False) if user is authenticated, else return (None,True). """
  78         
  79         
  80         
  81         
  82         import Cookie
  83         user = None  
  84         try_next = True  
  85         
  86         otherAppCookie = "MoinAuth" 
  87         try:
  88             cookie = Cookie.SimpleCookie(request.cookies) 
  89         except Cookie.CookieError:
  90             cookie = None 
  91 
  92         if cookie and otherAppCookie in cookie: 
  93             import urllib
  94             if sys.version_info[:2] > (2, 5):
  95                 cookievalue = cookie[otherAppCookie].value 
  96             else:
  97                 cookievalue = cookie[otherAppCookie] 
  98             
  99             
 100             
 101             
 102             cookievalue = cookievalue[1: -1] 
 103             
 104             cookievalues = cookievalue.split('#') 
 105 
 106             email = aliasname = sessionid = ''
 107             try:  
 108                 auth_username = cookievalues[0] 
 109                 email = cookievalues[1] 
 110                 aliasname = cookievalues[2] 
 111                 sessionid = cookievalues[3] 
 112             except IndexError: 
 113                 pass  
 114             
 115             
 116             
 117             
 118 
 119             
 120             if auth_username:
 121                 import hashlib  
 122                 sidHash = hashlib.md5(cookievalue).hexdigest() 
 123                 
 124                 sidOK = verifySession(sidHash) 
 125                 if not sidOK:
 126                     auth_username = None
 127             
 128             
 129             if auth_username:
 130                 
 131                 from MoinMoin.user import User
 132                 
 133                 user = User(request, name=auth_username, auth_username=auth_username, auth_method=self.name)
 134                 changed = False
 135                 if email != user.email: 
 136                     user.email = email ; 
 137                     changed = True 
 138                 
 139                     
 140                     
 141 
 142                 if user:
 143                     user.create_or_update(changed)
 144                 if user and user.valid: 
 145                     try_next = False 
 146         
 147         return user, try_next 
 148 
 149 from MoinMoin.config import multiconfig, url_prefix_static
 150 
 151 class Config(multiconfig.DefaultConfig):
 152 
 153 
 154     auth = [ExternalCookie(autocreate=True)] 
 155     
 156     
 157     user_form_disable = ['name', 'aliasname', 'email',] 
 158     user_form_remove = ['password', 'password2', 'css_url', 'logout', 'create', 'account_sendmail','jid'] 
 159     
 160     cookie_lifetime = (12, 12)   
 161 
 162 

Initial Testing

If you use the Firefox browser and have the Web Developer addon extension installed, initial testing will be fast and painless. Log on to your other application and click on Tools... Web Developer... Cookies... View Cookie Information. You will probably find at least one cookie that looks like a session identifier created by your application at login, usually these will have a value with a large random number and perhaps a time stamp.

Next, click on Tools... Web Developer... Cookies... Add Cookie. Give the cookie a name of MoinAuth (case sensitive). Set the value to yourname#youremail@yourprovider.com with no spaces, and be sure to use the # character as a separator. If your other application and the wiki run on the same host, set the host to the same value used by your other application (if not, omit the host from the domain name to share cookies across hosts). Set the path value to "/" without the quotes. Click the Session Cookie check box and click save.

Open a second browser window and load your starting wiki page. The wiki should recognize you as a logged in user. Do a quick test to verify that you can edit and save a wiki page and verify that you can change your User Preferences.

Changing the Other Application

The example external_cookie method expects the cookie value to contain several pieces of information separated with the # character:

• the wiki user id -- always required

• the user's email address -- needed if the user is to be able to update and save MoinMoin User Preferences

• user alias -- usually not required, used to override user IDs that are not wiki-like user names
• unique session ID -- a big random number or timestamp and random number

Your application must store the MoinAuth cookie with a path set to '/'. Setting the path to '/' is normally not recommended because it presents a small security risk. It allows an application to read the cookies created by a different application. In this case, that is exactly our intent -- MoinMoin must be able to read the cookies set by the other application.

As you have already demonstrated to yourself above, any user with the skill to install the Firefox Web Developer addon could easily create a cookie and hack his way into the wiki using someone else's ID. To prevent this from happening, MoinMoin will need to validate the cookie value against an entry in a secure shared storage area created by the other application.

We want to avoid creating a potential new security issue by building a cross-reference of user ID to session ID or even a list of session IDs that might be of use to a hacker. A better way is for your application to hash (not encrypt) the MoinAuth cookie value and store the result in a secure shared storage area. Add a timestamp to each entry so obsolete entries can be removed later.

There is commented out code in the example wikiconfig.py to perform a hash of the cookie contents and validate the result against a MySQL table. In addition, there is alternative commented out code that will delete entries from the MySQL table that are more than 4 hours old, validate the hashed cookie value against the table and update the timestamp. A better method is to modify the other application to remove obsolete entries from the table, perhaps each time a user logs in.

As you begin to modify your application almost all of your testing can be done with the Firefox Web Developer extension. Before you login to the other application there should be no MoinAuth cookie, after login there should be a MoinAuth cookie, after logout there should be no cookie. In addition, the shared storage area should be updated with a new hashed cookie value after login and cleared after logout. Accessing a wiki page after you are logged in will cause moin to create a MOIN_SESSION cookie.

Modifying themes

The next step is to modify the login and logout links in the navigation area of wiki pages. If you limit your users to one theme, modify the code below to point to your other application's login and logoff pages. If you allow users to choose from among several themes, it may be easiest to modify the /MoinMoin/theme/init.py script directly.

If you always log on to your other application before accessing a wiki page, this modification and the one following are not required. If you comment out the login_inputs and logout_possible variables near the top of the ExternalCookie class, then your wiki pages will not contain login and logout hyperlinks.

The code below is for moin 1.9.

   1     def username(self, d):
   2         """ Assemble the username / userprefs link
   3         
   4         @param d: parameter dictionary
   5         @rtype: unicode
   6         @return: username html
   7         """
   8         request = self.request
   9         _ = request.getText
  10 
  11         userlinks = []
  12         
  13         
  14         if request.user.valid and request.user.name:
  15             interwiki = wikiutil.getInterwikiHomePage(request)
  16             name = request.user.name
  17             aliasname = request.user.aliasname
  18             if not aliasname:
  19                 aliasname = name
  20             title = "%s @ %s" % (aliasname, interwiki[0])
  21             
  22             homelink = (request.formatter.interwikilink(1, title=title, id="userhome", generated=True, *interwiki) +
  23                         request.formatter.text(name) +
  24                         request.formatter.interwikilink(0, title=title, id="userhome", *interwiki))
  25             userlinks.append(homelink)
  26             
  27             if 'userprefs' not in self.request.cfg.actions_excluded:
  28                 userlinks.append(d['page'].link_to(request, text=_('Settings'),
  29                                                querystr={'action': 'userprefs'}, id='userprefs', rel='nofollow'))
  30 
  31         if request.user.valid:  
  32             if request.user.auth_method in request.cfg.auth_can_logout:
  33                 userlinks.append('<a href="/myapp/Logout">%s</a>' % _('Logout', formatted=False)) 
  34         else:
  35             query = {'action': 'login'}
  36             
  37             if request.cfg.auth_login_inputs == ['special_no_input']:
  38                 query['login'] = '1'
  39             if request.cfg.auth_have_login:
  40                 userlinks.append('<a  href="/myapp/Login">%s</a>' % _("Login", formatted=False)) 
  41 
  42         userlinks = [u'<li>%s</li>' % link for link in userlinks]
  43         html = u'<ul id="username">%s</ul>' % ''.join(userlinks)
  44         return html

Modifying the Application Login Page

As a final touch, you may want to consider modifying your login page for wiki users who decide to login from a wiki page. This depends upon your choice of web servers, but most will pass something similar to an HTTP_REFERER field which will contain the prior URL.

Check this value to determine if the referrer page was a wiki page, if so save the URL and at the end of a successful logon either redirect the current page back the referring wiki page or open a new window with the URL of the referring page.