MSNT Auth v2.0.1
Squid web proxy Authentication module
Antonino Iannella, Stellar-X Pty Ltd
Fri Sep 29 15:53:33 CST 2000

Introduction

This is an authentication module for the Squid proxy server to authenticate users on an NT domain.

It originates from the Samba and SMB packages by Andrew Tridgell and Richard Sharpe. This version is sourced from the Pike authentication module by William Welliver (hwellive@intersil.com).

Usage is simple. It accepts a username and password on standard input and will return OK if the username/password is valid for the domain, or ERR if there was some problem. Check syslog messages for reported problems.

Make any changes to the source code you need.

Type 'make', then 'make install', then 'make clean'.

To avoid using the makefile, it may compile with gcc -O2 -s -o msntauth *.c

'Make install' will put 'msntauth' into /usr/local/squid/bin by default.

The Makefile uses the GCC compiler, and assumes that it is in the current PATH. Msntauth is known to compile properly on Redhat Linux 6, and FreeBSD 3.1 without problems. Other operating systems are untested, but use a recent copy of the GNU C compiler. Smbencrypt.c has the '#include ' line commented out. Remove the comment for S5R4 systems, like Solaris.

Msntauth uses a configuration file which is a break from previous releases. The file is /usr/local/squid/etc/msntauth.conf. If this needs to be changed, it is defined in confload.h.

An example configuration file is provided. It looks like

# Sample MSNT authenticator configuration file
# Antonino Iannella, Stellar-X Pty Ltd
# Tue Sep 26 17:26:59 CST 2000

server my_PDC           my_BDC          my_NTdomain
server other_PDC        other_BDC       otherdomain

denyusers       /usr/local/squid/etc/denyusers
allowusers      /usr/local/squid/etc/allowusers

All comments start with '#'.

NT servers are used to query user accounts. The 'server' lines are used for this, with the PDC, BDC, and NT domain as parameters. Up to 5 servers/domains can be queried. If this is not enough modify the MAXSERVERS define in confload.h. At least one server must be specified, or msntauth will not run.

When a user provides a username/password, each of these servers will be queried to authenticate the username. It stops after a user has been successfully authenticated, so it makes sense to specify the most commonly queried server first. Make sure the servers can be reached and are active, or else msntauth will start failing user accounts!

Users who are not allowed to access the web proxy can be added to the denied user list. This list is read around every minute, or when the msntauth process receives a SIGHUP signal.

The denied user file is set using the 'denyusers' directive in msntauth.h. The denied user file contains a list of usernames in no particular structure or form. If the file does not exist, no users are denied. The file must be readable by the web proxy user.

Similar to denying users, you can allow users to access the proxy by username. This is useful if only a number of people are allowed supposed to be accessing a proxy.

The allowed user file is set using the 'allowusers' directive in msntauth.h. If the file does not exist or if empty, all users are allowed.

You could make use of the SHOWMBRS tool in Microsoft Technet. This gives you a list of users which are in a particular NT Domain Group. This list can be made into the allowed users file.

Some other rules -

1. The operation of the denied user file is independent of the allowed user file. The former file is checked first.
2. You can use none, one, or both files.
3. If a username appears in the denied user file, they will be denied, even if they are in the allowed user file.
4. If a username is not in either file, they will be denied, because they have not been allowed.
5. If the allowed user file is in use and is empty, all users will be allowed.

Refer to Squid documentation for the required changes to squid.conf. You will need to set the following lines to enable authentication for your access list -

  acl  proxy_auth REQUIRED
  http_access allow password
  http_access allow 
  http_access deny all

You will also need to review the following directives -

  proxy_auth_realm enterprise web gateway
  authenticate_program /usr/local/squid/bin/msntauth
  authenticate_ttl 5
  authenticate_children 20

Testing

I strongly urge that Msntauth is tested prior to being used in a production environment. It may behave differently on different platforms. To test it, run it from the command line. Enter username and password pairs separated by a space.

It should behave in the following way -

 - Press ENTER to get an OK or ERR message.
 - Make sure pressing CTRL-D behaves the same as a carriage return.
 - Make sure pressing CTRL-C aborts the program.
 - Test that entering no details does not result in an OK or ERR message.
 - Test that entering an invalid username and password results in
   an ERR message. Note that if NT guest user access is allowed on
   the PDC, an OK message may be returned instead of ERR.
 - Test that entering an valid username and password results in an OK message.
   Try usernames which are and aren't in the denied/allowed user files,
   if they're in use.
 - Test that entering a guest username and password returns the correct response.

To contact the maintainer of this package, email Antonino Iannella at antonino@usa.net, antonino.iannella@usa.net, or antonino.iannella@camtech.com.au.

For an unknown username, Msntauth returns OK. This is because the PDC returns guest access for unknown users, even if guest access is disabled. This problem was reported by Mr Vadim Popov (vap@iilsr.minsk.by). I am not able to replicate this.

The tested environment consisted of PDC on Windows NT 4, SP 6. Squid 2.3 and Msntauth was tested on SuSe, RedHat, and Debian Linux. A fix was provided in case you have this problem. Apply the provided patch before compiling, using

  patch smblib.c < smblib.c.patch

Known limitation

Usernames are checked if they are allowed or denied. If a username is found as a substring of a different username in these files, the user will be affected somehow. For example, if 'jpeterman' has been explicitly denied in the denyusers file, then 'jpeter' who is trying to use the proxy, will be denied. If this causes anyone any problems, then I'll fix it.

The following list of changes have been made to improve msntauth. I have not had a chance to do too much testing due to lack of resources. There should be no problems, though.

• Added many patches from Duane Wessels to stop compilation errors (?)
• Improved the main() function yet again
• Created a more informative Makefile
• Added an 'allowed users' feature to complement the 'denied users' feature
• Stopped the use of alarm() which was causing problems under Solaris
• Added more syslog messages for authentication problems
• Added the use of a configuration file, instead of hard-coding NT server details
• Allowed for querying multiple NT servers and domains (this was a hot issue)
• Changed README into an HTML document to improve readability
• Didn't make use of GNU autoconf. I will in future, I promise.
• Removed denied/allowed username substring search limitation.

Hopefully msntauth and Squid is now a more valuable product. Feel free to send me success or problem stories.