= RubyCAS-Client

Author::    Matt Zukowski <matt AT roughest DOT net>; inspired by code by Ola Bini <ola.bini AT ki DOT se> and Matt Walker <mwalker AT tamu DOT edu>
Copyright:: (c) 2008 Urbacon Ltd.
License::   GNU Lesser General Public License v2.1 (LGPL 2.1)
Website::   http://code.google.com/p/rubycas-client and http://rubyforge.org/projects/rubycas-client


=== RubyCAS-Client is a Ruby client library for Yale's Central Authentication Service (CAS) protocol.

CAS provides a secure single sign on solution for web-based applications. The user logs in to your
organization's CAS server, and is automatically authenticated for all other CAS-enabled applications.

For general information about the open CAS protocol, please have a look at http://www.ja-sig.org/products/cas.

If your organization does not already have a CAS server, you may be interested in RubyCAS-Client's sister project,
RubyCAS-Server[http://code.google.com/p/rubycas-server/].


== Getting help and reporting problems

If you need help, try posting to the RubyCAS discussion group at http://groups.google.com/group/rubycas-server.

To report problems, please use the Google Code issue tracker at http://code.google.com/p/rubycas-client/issues/list.


== Installation

You can download the latest version of RubyCAS-Client from the project's rubyforge page at 
http://rubyforge.org/projects/rubycas-client.

However, it is easier to install the CAS client into a Ruby on Rails app as a plugin:

  cd <your rails app>
  ./script/plugin install http://rubycas-client.googlecode.com/svn/trunk/rubycas-client

Alternatively, the library is also installable as a RubyGem[http://rubygems.org]:

  gem install rubycas-client
  
If your Rails application is under Subversion control, you can also install the plugin as an svn:external, ensuring that
you always have the latest bleeding-edge version of RubyCAS-Client:

  ./script/plugin install -x http://rubycas-client.googlecode.com/svn/trunk/rubycas-client


== Usage Examples

Although RubyCAS-Client can be used with other web Frameworks (for example Camping), the following examples
are aimed at {Ruby on Rails}[http://rubyonrails.org].

==== Using RubyCAS-Client in Rails controllers

<i>Note that from this point on we are assuming that you have a working CAS server up and running!</i>

After installing RubyCAS-Client as a plugin (see above), add the following to your app's <tt>config/environment.rb</tt>
(make sure that you put it at the bottom of the file, *after* the Rails Initializer):
  
  CASClient::Frameworks::Rails::Filter.configure(
    :cas_base_url => "https://cas.example.foo/"
  )
  
(Change the <tt>:cas_base_url</tt> value to your CAS server's base URL; also note that many CAS servers are configured
with a base URL that looks more like "https://cas.example.foo/cas".)

Then, in your <tt>app/controllers/application.rb</tt> (or in whichever controller you want to add the CAS filter for):

  before_filter CASClient::Frameworks::Rails::Filter
  
That's it. You should now find that you are redirected to your CAS login page whenever you try to access any action
in your protected controller. You can of course qualify the <tt>before_filter</tt> as you would with any other ActionController
filter. For example: 

  before_filter CASClient::Frameworks::Rails::Filter, :except => [ :unprotected_action, :another_unprotected_action ]

<b>Once the user has been authenticated, their authenticated username is available under <tt>session[:cas_user]</tt>,</b>
If you want to do something with this username (for example load a user record from the database), you can append another 
filter method that checks for this value and does whatever you need it to do.

<b>Note:</b> If Rails complains about missing constants, try adding this before the CASClient configuration:

  require 'casclient'
  require 'casclient/frameworks/rails/filter'


==== A more complicated example

Here is a more complicated configuration showing most of the configuration options along with their default values
(this does not show proxy options, which are covered in the next section):

  # enable detailed CAS logging
  cas_logger = CASClient::Logger.new(RAILS_ROOT+'/log/cas.log')
  cas_logger.level = Logger::DEBUG

  CASClient::Frameworks::Rails::Filter.configure(
    :cas_base_url  => "https://cas.example.foo/",
    :login_url     => "https://cas.example.foo/login",
    :logout_url    => "https://cas.example.foo/logout",
    :validate_url  => "https://cas.example.foo/proxyValidate",
    :username_session_key => :cas_user,
    :extra_attributes_session_key => :cas_extra_attributes
    :logger => cas_logger,
    :authenticate_on_every_request => true
  )

Note that normally it is not necessary to specify <tt>:login_url</tt>, <tt>:logout_url</tt>, and <tt>:validate_url</tt>.
These values are automatically set to standard CAS defaults based on the given <tt>:cas_base_url</tt>.

The <tt>:username_session_key</tt> value determines the key under which you can find the CAS username in the Rails session hash.

Any additional info that the CAS server might have supplied about the user during authentication will be found under the
<tt>:extra_attributes_session_key</tt> value in the Rails session hash (i.e. given the above configuration, you would find this
info under <tt>session[:cas_extra_attributes]</tt>).

An arbitrary Logger instance can be given as the :logger parameter. In the example above we log all CAS activity to a 
<tt>log/cas.log</tt> file in your Rails app's directory.

==== Re-authenticating on every request (i.e. the "single sign-out problem")

By default, the Rails filter will only authenticate with the CAS server when no session[:cas_user] value exists. Once the user 
has been authenticated, no further CAS forwarding is done until the user's session is wiped. This saves you
the trouble of having to do this check yourself (since in most cases it is not advisable to go through the CAS server
on every request -- this is slow and would potentially lead to problems, for example for AJAX requests). However,
the disadvantage is that the filter no longer checks to make sure that the user's CAS session is still actually open.
In other words it is possible for the user's authentication session to be closed on the CAS server without the
client application knowing about it.

In the future RubyCAS-Client will support the new "Single Sign-Out" functionality in CAS 3.1, allowing the server to 
notify the client application that the CAS session is closed, but for now it is up to you  to handle this by, for example, 
by wiping the local <tt>session[:cas_user]</tt> value periodically to force a CAS re-check.
 
Alternatively, it is possible to disable this authentication persistence behaviour by setting the <tt>:authenticate_on_every_request</tt>
configuration option to true as in the example above.


==== Defining a 'logout' action

Your Rails application's controller(s) will probably have some sort of logout function. Here you can do any necessary local
cleanup, and then call <tt>CASClient::Frameworks::Rails::Filter.logout(controller)</tt>. For example:

  class ApplicationController < ActionController::Base
    
    # ...
  
    def logout
      # optionally do some local cleanup here
      # ...
      
      CASClient::Frameworks::Rails::Filter.logout(self)
    end
  end

By default, the logout method will clear the local Rails session, do some local CAS cleanup, and redirect to the CAS
logout page. Additionally, the <tt>request.referer</tt> value from the <tt>controller</tt> instance is passed to the
CAS server as a 'destination' parameter. This allows RubyCAS server to provide a follow-up login page allowing
the user to log back in to the service they just logged out from using a different username and password. Other
CAS server implemenations may use this 'destination' parameter in different ways. 

==== Gatewayed (i.e. optional) authentication

"Gatewaying" essentially allows for optional CAS authentication. Users who already have a pre-existing CAS SSO session 
will be automatically authenticated for the gatewayed service, while those who do not will be allowed to access the service 
without authentication. This is useful for example when you want to show some additional private content on a homepage to 
authenticated users, but also want anonymous users to be able to access the page without first logging in.

To allow users to access a page without authenticatin, simply use <tt>CASClient::Frameworks::Rails::GatewayFilter</tt>
in place of <tt>CASClient::Frameworks::Rails::Filter</tt> in your controller. For example, you may want to require
CAS authentication for all actions in a controller except the index action:

  class ExampleController < ApplicationController
    before_filter CASClient::Frameworks::Rails::GatewayFilter, :only => :index
    before_filter CASClient::Frameworks::Rails::Filter, :except => :index
    
    # ...
  end
  

==== How to act as a CAS proxy

CAS 2.0 has a built-in mechanism that allows a CAS-authenticated application to pass on its authentication to other applications.
An example where this is useful might be a portal site, where the user logs in to a central website and then gets forwarded to
various other sites that run independently of the portal system (but are always accessed via the portal). The exact mechanism
behind this is rather complicated so I won't go over it here. If you wish to learn more about CAS proxying, a great walkthrough
is available at http://www.ja-sig.org/wiki/display/CAS/Proxy+CAS+Walkthrough.

RubyCAS-Client fully supports proxying, so a CAS-protected Rails application can act as a CAS proxy.

Additionally, RubyCAS-Client comes with a controller that can act as a CAS proxy callback receiver. This is necessary because
when your application requests to act as a CAS proxy, the CAS server must contact your application to deposit the proxy-granting-ticket
(PGT). Note that in this case the CAS server CONTACTS YOU, rather than you contacting the CAS server (as in all other CAS operations).

Confused? Don't worry, you don't really have to understand this to use it. To enable your Rails app to act as a CAS proxy, 
all you need to do is this:

In your <tt>config/environment.rb</tt>:

  # enable detailed CAS logging for easier troubleshooting
  cas_logger = CASClient::Logger.new(RAILS_ROOT+'/log/cas.log')
  cas_logger.level = Logger::DEBUG

  CASClient::Frameworks::Rails::Filter.configure(
    :cas_base_url => "https://cas.example.foo/",
    :proxy_retrieval_url => "https://cas-proxy-callback.example.foo/cas_proxy_callback/retrieve_pgt",
    :proxy_callback_url => "https://cas-proxy-callback.example.foo/cas_proxy_callback/receive_pgt",
    :logger => cas_logger
  )
  
In <tt>config/routes.rb</tt> make sure that you have a route that will allow requests to /cas_proxy_callback/:action to be routed to the
CasProxyCallbackController. This should work as-is with the standard Rails routes setup, but if you have disabled the default
route, you should add the following:

  map.cas_proxy_callback 'cas_proxy_callback/:action', :controller => 'cas_proxy_callback'
  
Now here's a big giant caveat: <b>your CAS callback application and your CAS proxy application must run on separate Rails servers</b>.
In other words, if you want a Rails app to act as a CAS ticket-granting proxy, the cas_proxy_callback controller
must run on a different server. This is because Rails does not properly support handling of concurrent requests. The CAS proxy mechanism
acts in such a way that if your proxy application and your callback controller were on the same server
you would end up with a deadlock (the CAS server would be waiting for its callback to be accepted by your Rails server,
but your Rails server wouldn't respond to the CAS server's callback until the CAS server responded back first).

The simplest workaround is this:

1. Create an empty rails app (i.e. something like <tt>rails cas_proxy_callback</tt>)
2. Make sure that you have the CAS plugin installed. If you installed it as a gem, you don't have to do anything since
   it is already installed. If you want to install as a plugin, see the instructions in the "Installing" section above.
3. Make sure that the server is up and running, and configure your proxy_callback_url and proxy_retrieval_url to point
   to the new server as described above (or rather, make Pound point to the new server, if that's how you're handling https).
   
That's it. The proxy_callback_controller doesn't require any additional configuration. It doesn't access the database
or anything of that sort.

Once your user logs in to CAS via your application, you can do the following to obtain a service ticket that can then be used
to authenticate another application:

  service_uri = "http://some-other-application.example.foo"
  proxy_granting_ticket = session[:cas_pgt]
  ticket = CASClient::Frameworks::Rails::Filter.client.request_proxy_ticket(service_uri, proxy_granting_ticket).ticket
  
<tt>ticket</tt> should now contain a valid service ticket. You can use it to authenticate other services by sending it and 
the service URI as parameters to your target application:

  http://some-other-application.example.foo?service=#{CGI.encode(ticket.target_service)}&ticket=#{ticket.proxy_ticket}
  
This is of course assuming that http://some-other-application.example.foo is also protected by the CAS filter. 
Note that you should always URI-encode your service parameter inside URIs!

Note that #request_proxy_ticket returns a CASClient::ProxyTicket object, which is why we need to call #ticket on it 
to retrieve the actual service ticket string.

===== Additional proxying notes and caveats

<b>The proxy url must be an https address.</b> Otherwise CAS will refuse to communicate with it. This means that if you are using
the bundled cas_proxy_callback controller, you will have to host your application on an https-enabled server. This can be a bit
tricky with Rails. WEBrick's SSL support is difficult to configure, and Mongrel doesn't support SSL at all. One workaround is to
use a reverse proxy like Pound[http://www.apsis.ch/pound/], which will accept https connections and locally re-route them
to your Rails application. Also, note that <i>self-signed SSL certificates likely won't work</i>. You will probably need to use
a real certificate purchased from a trusted CA authority (there are ways around this, but good luck :)


== SSL Support

Make sure you have the Ruby OpenSSL library installed. Otherwise you may get errors like:

  no such file to load -- net/https

To install the library on an Debian/Ubuntu system:

  sudo apt-get install libopenssl-ruby

For other platforms you'll have to figure it out yourself.



== License

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU Lesser General Public License
along with this program (see the file called LICENSE); if not, write to the
Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA