How can I install the $0 applications from the Ubuntu Software Center with apt-get?

In the Ubuntu Software Center, there are lots of $0 apps that I can 'purchase': for example:

crazytoad

pinball-bakno

colorsudoku

As these applications are free (as in beer), I wonder how I can install them using apt-get.

First the rant: you made me use the USC!

Now the answer: Not all the software included in the USC can be distributed, the same way as free (as freedom) applications. These are the so called privative apps. These apps are not included in the regular Ubuntu repositories, nor they are accessible through normal software channels, but trough repositories called private/commercial PPA's, that needs authentication, which is managed by the USC.

These mechanisms are hidden from the normal user, but since the USC is a free (as freedom) application, you can dissect it and see it's internals, though truth be told, just launching USC from the terminal suffice. As example I'll be showing the repository of 'crazytoad':

softwarecenter.backend - INFO - add_repo_add_key_and_install_app() 'private-ppa.launchpad.net/commercial-ppa-uploaders/crazytoad/ubuntu raring main' '<hereissomeidthatIhadtoscrub' 'crazytoad'

As you can see private-ppa.launchpad.net is the main domain for... private ppa's. If you try to access the site using your browser, it will ask you for authentication (remembers the user/password pair you gave the first time you downloaded an app?) which isn't your Ubuntu One username and password, but a Token pair created by USC with the help of the OpenID protocol.

So, how to install free as beer apps using apt-get? You first have to find out the repository:

apt-cache policy crazytoad
crazytoad:
  Installed: (none)
  Candidate: 2.0.0-0ubuntu1
  Version table:
     2.0.0-0ubuntu1 0
        500 https://private-ppa.launchpad.net/commercial-ppa-uploaders/crazytoad/ubuntu/ raring/main amd64 Packages

and login using the Ubuntu Software Center. Otherwise, you can not.

After checking my mail, I found out the authentication credentials to add to my sources.list:

deb https://myuser:[email protected]/commercial-ppa-uploaders/crazytoad/ubuntu raring main

I just have to add the GPG key, modify the crazytoad and I'm all set up for Rock & Roll.