3.4 Now something More Complicated

3.4 Now something More Complicated - Authentication

Now that you know how to write a primitive handler, let's try something more complicated.

Let's say we want to password-protect this directory. We want the login to be "spam", and the password to be "eggs".

First, we need to tell Apache to call our authentication handler when authentication is needed. We do this by adding the PythonAuthenHandler. So now our config looks like this:

  <Directory /mywebdir>
      AddHandler mod_python .py
      PythonHandler myscript
      PythonAuthenHandler myscript
      PythonDebug On
  </Directory>

Notice that the same script is specified for two different handlers. This is fine, because if you remember, mod_python will look for different functions within that script for the different handlers.

Next, we need to tell Apache that we are using Basic HTTP authentication, and only valid users are allowed (this is fairly basic Apache stuff, so we're not going to go into details here). Our config looks like this now:

  <Directory /mywebdir>
     AddHandler mod_python .py
     PythonHandler myscript
     PythonAuthenHandler myscript
     PythonDebug On
     AuthType Basic
     AuthName "Restricted Area"
     require valid-user
  </Directory>

Now we need to write an authentication handler function in myscript.py. A basic authentication handler would look like this:

from mod_python import apache

def authenhandler(req):

    pw = req.get_basic_auth_pw()
    user = req.user

    if user == "spam" and pw == "eggs":
       return apache.OK
    else:
       return apache.HTTP_UNAUTHORIZED

Let's look at this line by line:

def authenhandler(req):

This is the handler function declaration. This one is called authenhandler because, as we already described above, mod_python takes the name of the directive (PythonAuthenHandler), drops the word "Python" and converts it lower case.

    pw = req.get_basic_auth_pw()

This is how we obtain the password. The basic HTTP authentication transmits the password in base64 encoded form to make it a little bit less obvious. This function decodes the password and returns it as a string. Note that we have to call this function before obtaining the user name.

    user = req.user

This is how you obtain the username that the user entered.

    if user == "spam" and pw == "eggs":
        return apache.OK

We compare the values provided by the user, and if they are what we were expecting, we tell Apache to go ahead and proceed by returning apache.OK. Apache will then consider this phase of the request complete, and proceed to the next phase. (Which in this case would be handler() if it's a .py file).

    else:
        return apache.HTTP_UNAUTHORIZED

Else, we tell Apache to return HTTP_UNAUTHORIZED to the client, which usually causes the browser to pop a dialog box asking for username and password.