Wednesday, January 21, 2015

Single Sign On from Apache in Django using Active Directory and LDAP

So you have a nice and shiny new Django application, you successfully transitioned from development to production, and now you want to add Single Sign On (SSO) so users can use the same credentials they already use somewhere else. Sounds good, how do you do it?


This is surprisingly easy, although there is some new syntax to learn, and you will need to get some info from your system administrator. Here are some steps for Apache-2.4 from ApacheLounge.
  1. Follow the directions in the Django documentation on Authentication using REMOTE_USER and add RemoteUserMiddleware and RemoteUserBackend to AUTHENTICATION_BACKENDS to your settings file. This will use the REMOTE_USER environment variable set by Apache when it authorizes users and use it for authentication on the Django website.
  2. Note: This will change how Django works; for example, any authorized user not in the Django Users model will have their username automatically added and set to active, but their password and the is_staff attribute will not be set.

  3. Get the URL or IP address of your Active Directory server from your system administrator. For LDAP with basic authentication, the port is usually 389, but check to make sure.
  4. Also get the "Distringuished Name" of the "search base" from your system administrator. A "Distringuished Name" is LDAP lingo for a string made up of several components, usually the "Organizational Unit (OU)" and the "Domain Components (DC)", that distinguish entries in the Active Directory.
  5. Finally ask your system administrator to set up a "binding" distinguished name and password to authorize searches of the Active Directory.
  6. Then in httpd.conf enable mod_authnz_ldap and mod_ldap.
  7. Also in httpd.conf add a Location for the URL endpoint, EG: / for the entire website, to be password protected.
  8. You must set AuthName. This will be displayed to the user when they are prompted to enter their credentials.
  9. Also must also set AuthType, AuthBasicProvider, AuthLDAPUrl and Require. Prepend ldap:// to your AD server name and append the port, base DN, scope, attribute and search filter. The port is separated by a colon (:), the base DN by a slash (/) and the other parameters by question marks (?) such as:
  10. <Location />
      AuthName "Please enter your SSO credentials."
      AuthBasicProvider ldap
      AuthType basic
      AuthLDAPUrl "ldap://,DC=activedirectory,DC=com?sAMAccountName"
      AuthLDAPBindDN "CN=binding_account,OU=Administrators,DC=activedirectory,DC=com"
      AuthLDAPBindPassword binding_password
      LDAPReferrals off
      Require valid-user
  11. The "attribute" to search for in Windows Active Directory is "SAM-Account-Name" or sAMAccountName. This is the equivalent of a user name.
  12. The default "scope" is sub which means it will search the base DN and everything below it in the Active Directory. And the default "filter" is (objectClass=*) which is the equivalent of no filter.
  13. There are several options for limiting users and groups. If you set Require to valid-user then any user in the AD who can authenticate will be authorized.
  14. Set AuthLDAPBindDN and AuthLDAPBindPassword to the binding account's DN and password.
  15. It has been reported that LDAPReferrals should be set to off or you may get the following error.

    (70023)This function has not been implemented on this platform: AH01277: LDAP: Unable to add rebind cross reference entry. Out of memory?

  16. Finally, restart your Apache httpd server and test out your site.
Now when users go to your Django site, when they open the location that requires authentication they will see a pop up that asks for their credentials.


In addition to adding authenticated users to the Django Users model, the users credentials are stored in the browser. This makes logging out akward since the user will need to close their browser to logout. There are several approaches to get Django to logout a user.
  • redirect the user to a URL with fake basic authentication prepended to the path.
  • render a template with status set to 401 which is the code for unauthorized that will clear the credentials in browser cache.
  • from django.shortcuts import render
    from django.contrib.auth import logout as auth_logout
    import logging  # import the logging library
    logger = logging.getLogger(__name__)  # Get an instance of a logger
    def logout(request):
        Replaces ``django.contrib.auth.views.logout``.
        logger.debug('user %s logging out', request.user.username)
        return render(request, 'index.html', status=401)

Using Telnet to ping AD server

A lot of sites suggest this. First you will need to enable Telnet on your Windows PC. This can be done from Uninstall a program in the Control Panel by selecting Turn Windows features on or off and checking Telnet Client. Then opening a command terminal and typing telnet followed by open 389. Surprise! If it works you will only see the output:
Connecting to
If it does not work then you will see this additional output:
Could not open connection to the host, on port 389: Connect failed
Now treat yourself and try open Use control + ] to kill the connection, then type quit to quit telnet.

Testing LDAP using Python

  • Python-LDAP
  • So to learn more about LDAP there are a couple of packages that you can use to interrogate and authenticate with and AD server using LDAP. Python-LDAP seems to be common and easy to use. It's based on OpenLDAP.
    >>> import ldap
    >>> server = ldap.initialize('ldap://')
    >>> server.simple_bind('CN=bind_user,OU=Administrators,DC=activedirectory,DC=com','bind_password')  # returns 1 on success
    >>> user = l.search_s('OU=Users,DC=activedirectory,DC=com',ldap.SCOPE_SUBTREE,'(&(sAMAccountName=my_username)(ObjectClass=user))',('cn','sAMAccountName','mail'))
    >>> user
    [('CN=My Name,OU=Super-Users,OU=USA,OU=California,OU=Sites,DC=activedirectory,DC=com',
      {'cn': ['My Name'],
       'sAMAccountName': ['my_username'],
       'mail': ['']})]
  • PyAD
  • Another Python package that can use LDAP to search an active directory is PyAD which uses PyWin32 and ADSI on Windows.
  • PyWin32
  • The only decent documentation for this is Tim Golden's website.


  • If users will only use the Django application on a Windows PC which they already have been authorized, EG through windows logon, then using either mod_authnz_sspi or mod_authnz_ntlm to acquire those credentials from your Windows session is also an option.
  • Django Extensions and Snippets
  • There are several Django extensions and snippets that use Python-LDAP and override ModelBackend so that Django handles authorization and authentication instead of Apache.

    Some Django extensions and snippets also exist to subclass ModelBackends to use PyWin32 to use local credentials from the current windows machine for authorization and authentication from within Django.

  • SAML and OAuth
  • Sure you could do this. You can also use SSL with LDAP or Kerebos with SSPI/NTLM. But, alas, I did not research these options althought I did come across a few references.

CSS and JS

The references section loosely based on Javascript TOC robot. It could also use the counters and the ::before style pseudo-element, but since I'm using JavaScript it doesn't make sense. But here's what that looked like anyway.
h2.references {counter-reset: refs;}
p.references:before {
  content: "[" counter(refs) "]";
  counter-increment: refs;
  margin-right: 5px;
  font-weight: bold;

Friday, January 9, 2015

Questionable Quantities in MATLAB

I am proud to introduce Quantities for MATLAB. Quantities is an units and uncertainties package for MATLAB. It is inspired by Pint, a Python package for quantities.


Clone or download the Quantities package to your MATLAB folder as +Quantities.


  1. Construct a units registry, which contains all units, constants, prefixes and dimensions.
  2.     >> ureg = Quantities.unitRegistry
      ureg = 
      Map with properties:
            Count: 279
          KeyType: char
        ValueType: any
  3. Optionally pass verbosity parameter to unitRegistry to see list of units loaded.
  4.     >> ureg = Quantities.unitRegistry('v',2)
  5. Units and constants can be indexed from the unitRegsitry using their name or alias in parentheses or as dot-notation. The unit, constant and quantity class all subclass to double so you can perform any operation on them. Combining a double with a unit creates a quantity class object.
  6.     >> T1 = 45*ureg('celsius') % index units using parentheses or dot notation
        T1 = 
           45 ± 0 [degC];
        >> T2 = 123.3*ureg.degC % index units by name or by alias
        T2 = 
               123.3 ± 0 [degC];
        >> heat_loss = ureg.stefan_boltzmann_constant*(T1^4 - T2^4)
        heat_loss = 
               -819814 ± 0 [gram*second^-3];
  7. Perform operations. All units are converted to base.
  8.     >> T2.to_base
        ans = 
               396.45 ± 0 [kelvin];
        >> heat_loss = ureg.stefan_boltzmann_constant*(T1.to_base^4 - T2.to_base^4)
        heat_loss = 
               -819814 ± 0 [gram*second^-3];
  9. Add uncertainty to quantities by calling constructor. Uncertainty is propagated using 1st order linear combinations.
  10.     >> T3 = Quantities.quantity(56.2, 1.23, ureg.degC)
        T3 = 
               56.2 ± 1.23 [degC];
        >> heat_loss = ureg.stefan_boltzmann_constant*(T1^4 - T3^4)
        heat_loss = 
               -86228.1 ± 9966.66 [gram*second^-3];
MATLAB Syntax Highlighter brush by Will Schleter

Tuesday, November 25, 2014

Convert Excel row-column reference to A1 in MATLAB

I'm sure there are many of these snippets out there. Here is yet another one.
>> rc2a1(23,196)
Enjoy. Please don't use it for evil.

Monday, October 20, 2014

NumPy in virtualenv on Windows-x64 with wheels

[UPDATE 2014-11-17] I am about to eat my own words, because Carl Kleffner has provided openBLAS dynamic libraries and headers that you can use to build NumPy>=1.91. The DLL is compiled using his static mingw-w64 GCC toolchain. From his site download 2014-08-28_OpenBLAS-0.2.12dev_PR440.7z and extract it into numpy/core folder of the NumPy-1.9.1 distribution. Then follow the directions on the OpenBLAS users Google Group. A wheel is my dropbox. You can check it's config in a Python interpreter by importing NumPy and calling If you have nose, you can also run its tests by calling numpy.test(). Thanks Carl and Xianyi, this is an important milestone in making powerful numerical software free and open-sourced.

I want you to repeat after me.
"You will never be able to build NumPy on Windows x64 without the Intel Compiler Suite."
OK, was that so hard? You may have briefly entertained pipe dreams of building NumPy with OpenBLAS binaries, but then reality sank in after NumPy fails to load with this sad traceback.
Traceback (most recent call last):
  File "", line 1, in 
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\", line 170, in 
    from . import add_newdocs
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\", line 13, in 
    from numpy.lib import add_newdoc
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\lib\", line 18, in 
    from .polynomial import *
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\lib\", line 19, in 
    from numpy.linalg import eigvals, lstsq, inv
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\linalg\", line 51, in 
    from .linalg import *
  File "c:\.virtualenvs\openblas\lib\site-packages\numpy\linalg\", line 29, in 
    from numpy.linalg import lapack_lite, _umath_linalg
ImportError: DLL load failed: The specified procedure could not be found
Everyone said, "use dependency walker," which you did, and it told you that ABI incompatibilities meant that NumPy had no idea how to call your libopenblas.dll functions, even though they were exported and supported by libgfortran-3.dll and libgcc_s_seh-1.dll and the right versions of msvcr90.dll which you found buried in winsxs.

You got briefly excited when you saw that Carl Kleffner is actually working on a solution to this by introducing a static GCC toolchain to compile NumPy with OpenBLAS (*), but then you had a sudden insight. Hasn't Christoph Gohlke already compiled these Python libraries using Intel's Math Kernel Library (MKL)? Why yes he has! And can't you convert a bdist_wininst to a wheel? Of course you can!
$ wheel convert numpy‑MKL‑‑amd64‑py2.7.exe
Now you can just pip install the wheels in your virtualenvs.
$ pip install -U numpy-1.8.2-cp27-none-win_amd64.whl
Get your wheels here: Thanks Christoph (and Carl and Xianyi)!

(* See UPDATE at the top of this post for more info on Carl Kleffners OpenBLAS version of NumPy.)

Thursday, October 16, 2014

Traveling login

When you sit down at a Windows PC and log in, you begin a Console session which differs from the session that starts when you log in remotely. There can only be one Console session, but there can be any number of remote sessions using terminal services. Why is this distinction important? Sometimes, you may need to transfer your login from a remote session to the Console, so that you can fool a service into thinking that you are actively logged into the Console. For example there is a free service named after a certain fish often served in sushi, Yellowtail, that will disconnect if it senses that you are no longer actively connected to a session.

Here's the trick:
  1. Log in remotely to the Console session.
  2. $ mstsc.exe /console /v:your-server-name
  3. Disconnect, but do not log out.
  4. Log in remotely to another session.
  5. $ mstsc.exe /v:your-server-name
  6. View the logged on users.
  7. $ query user
     my-user-name          console             0  Disc        none   10/16/2014 9:03 AM
    >my-user-name          rdp                 1  Active      none   10/16/2014 9:03 AM
  8. If this doesn't work try qwinsta
  9. $ qwinsta
     SESSIONNAME       USERNAME                 ID  STATE   TYPE        DEVICE
     console           my-user-name              0  Disc
    >rdp               my-user-name              1  Active
  10. Switch to the console.
  11. $ tscon 1 /dest:console

A dialog window will pop up stating that you have been logged off of the computer, because you have logged in somewhere else (duh, at the console!). You can still log back into the computer using Remote Desktop Connection. If you check the users again, you'll see that you are actively logged in twice! Your console login remains active. Mission accomplished.

Peer-To-Peer Virtual Private Network (P2P VPN)

Also known as SocialVPN, this is a network that is very similar to an ad-hoc or peer-to-peer local network between computers connected via LAN cables or WiFi, but connects instead via a VPN tunnel through the internet. There are several services that purport to offer free (or freemium) P2P VPN services.

  • Hamachi, named after a certain fish often served in sushi, Yellowtail, may be the most well known freemium P2P VPN service. It is extremely fast and reliable, but the free service is limited to 5 clients and will shut down if it detects that you have disconnected. Paid service offers up to 32 clients starting at $29/year. It is available on Windows, Mac and Linux. Although the Linux version is Beta it works fine.
  • NeoRouter is a freemium service that at least by there comparison chart, is superior to Hamachi, but I have not tried it. Domain hosting is offered by NeoRouter for $15/month for up to 15 clients, which is a lot more than Hamachi! However, users can set up there own NeoRouter Server, the client and server installation is the same package, which can host the NeoRouter domain. If the server does not have a public IP, then port forwarding must be configured, so there are some hoops to jump through. It is available on all platforms. A Professional version offers support.
  • Remobo was a free cloud service with a Pro version that offered support, but it is now offline.
  • Wippien
  • n2n
  • Gbridge
  • P2PVPN
  • IPOP SocialVPN
  • OpenVPN

Remote Desktop Connections from Linux to Windows using Hamachi

This is pretty straight forward.
  1. Download and install a Hamachi service on your Windows machine. You can create a profile at LogMeIn Central to monitor your Hamachi networks.
  2. Log in to the Windows machine and switch the login to the console leaving it active. You can check its status on your LogMeIn Central profile under My Networks.
  3. Download the beta Hamachi Linux version and install it on your Linux box. For Ubuntu, use the *.deb file and execute sudo dpkg -i logmein-hamachi_VERSION_PLATFORM.deb where VERSION and PLATFORM may differ.
  4. start hamachi
  5. $ sudo hamachi login
    logging in ....... ok
    $ sudo hamachi join MYNETWORK MYPASSWORD
    Joining MYNETWORK ........ ok
    $ sudo hamachi list
    * [MYNETWORK] capacity 2/5, subscription type: Free, owner:
        123-456-789  MYWINDOWSMACHINE  alias: not set
  6. Use the Hamachi network IP address to start remote desktop, my version of Ubuntu already had this installed, but if not use sudo apt-get install rdesktop.
  7. $ rdesktop
  8. When the windows opens, log into your windows machine. To get a full screen, use -f option. A graphical client is also available, use sudo apt-get install grdesktop to install.
  9. You can mount a share on the Windows machine.
  10. $ mkdir –p /home/my-linux-profile/winshare
    $ sudo mount –t cifs // /home/my-profile/winshare \
      –o username=myWindowsUsername,password=myWindowsPassword,domain=myWindowsDomain,rw
    $ cd /home/my-linux-profile/winshare
  11. Or use samba
    smb : \>
  13. Or use the Nautilus graphical file browser to mount and browse the shares on your Windows machine.
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