Archive for September, 2009

Alfresco, SSO, and LDAP Expiring Date Attribute

20090914 3 comments

Deciding where to handle authorization in a setup where Alfresco’s authentication is handled by CAS which itself authenticates against LDAP may not be as easy as it sounds. This post goes through some of the possibilities and one solution.

LDAP Authentication with an Expiration Date Attribute

On Alfresco version 2.x we extended the LDAPAuthenticationComponentImpl class to be able to evaluate an LDAP filter string, configurable via spring, which was used primarily for the purpose of determining whether the user’s access to Alfresco had expired, with the expiration date being stored as an LDAP attribute. So our file would contain something like:


and the extended Java class LDAPAuthenticationComponentImpl contained:

ctx = ldapInitialContextFactory.getInitialDirContext(bindDn, new String(password));

String authenticationFilter = String.format(

authenticationFilterFormat, new Object[]{userName, timestamp});

NamingEnumeration<SearchResult> answer =

authenticationSearchBase, authenticationFilter, userSearchCtls);

if (answer != null && answer.hasMoreElements()) {

setCurrentUser(escapeUserName(userName, escapeCommasInUid));


Once the expiration date was reached the user was denied access to the application.

Moving to Single Sign On

We’re now migrating to Alfresco 3.x and also have the need to move to a single sign on solution.  Jasig’s Central Authentication Service (CAS) was chosen as the implementation, requiring some changes to our expiration strategy.

In our previous configuration, authentication (is this user who they say they are) and authorization (is this user allowed to do x) were intertwined in our single custom LDAPAuthenticationComponentImpl class.  Any other applications authenticating against the same LDAP server could implement their own authentication/authorization methods.

CAS however is only concerned with authentication, not authorization, and applications utilizing it need to be able to decouple those functions, which is a better architecture in most cases anyway.

Our task then is to determine where in the authentication/authorization strategy we should handle this expiration authorization.

Choosing Where to Handle Authorization

Customize the CAS Server?

Modifying the CAS LDAP authentication handler wouldn’t be an appropriate place for our expiration authorization since all CAS services share the same authentication handler and other applications that have no notion of the Alfresco service or its expiration could be denied authentication.

We could try implementing a CAS authorizing serviceRegistryDao which would in theory allow the CAS server to determine if the user were authorized to use the service requested beyond just the Enabled and SSO Participant settings.  An authorization component could be defined that would make the authorization decision based on the service being requested and the user requesting it.  Each service could choose its authorization component as an option during setup in the CAS Service Management application.

CAS really wants the client/application to handle authorization though, so customizing the server doesn’t look like a recommended approach.

Customize Alfresco?

We could setup Alfresco’s authentication chain to talk to CAS, but in version 3.2 Alfresco has changed its authentication configuration to use the notion of Authentication Subsystems (which seems nicely implemented) and most documentation indicates that integration with something like CAS is best achieved by using mod_cas or mod_auth_cas in Apache web server, and since we’re already using Apache in front of Tomcat with mod_proxy_ajp that approach seems like a good fit.

Wait, Can a Hacker Just Spoof HTTP Headers?

It looks like AJP between Tomcat and the web server is responsible for parsing these protocol specific (non-HTTP) headers to find the remote user value and set that in Tomcat’s HttpServletRequest, so a hacker can’t just modify the headers in their browser and have that be translated into an authenticated user.

However, it is extremely important that your Tomcat connector be behind a firewall and only accept connections from known web servers.  Otherwise a hacker could set up their own web server with a bogus authentication mechanism which would add an authenticated user header in the AJP message, which in turn would translate to that user being signed in to a protected application.

mod_cas or mod_auth_cas?

With proper security in place we should be OK to use an Apache CAS module for authentication, but which one?


  • hasn’t been maintained in quite a while
  • has missing links all over the site
  • the documentation incorrectly states that “CAS stands for Common Authorization Service”
  • Jasig recommends against it

so, um, we’ll go with mod_auth_cas.

There’s a detailed wiki article on setting up Alfresco authentication through mod_auth_cas but our challenge is to determine where in the flow to inject our authorization.

Option 1: Extend Alfresco’s Request Authn to Grab CAS Attribute

The CAS server can return attributes to the client and if mod_auth_cas passes those attributes through mod_proxy_ajp to Tomcat and Alfresco then we may be able to modify the component which checks that header for the authenticated username, HTTPRequestAuthenticationFilter, to also look for the expiration date attribute and authorize or deny the user.

After modifying Tomcat’s example snoop application to show all headers and attributes:

java.util.Enumeration eH = request.getHeaderNames();
while (eH.hasMoreElements()) {
String headerName = (String) eH.nextElement();
out.print("Header <b>" + headerName + ": </b>");
out.print(request.getHeader(headerName) + "<br>");
java.util.Enumeration eA = request.getAttributeNames();
while (eA.hasMoreElements()) {
String attributeName = (String) eA.nextElement();
out.print("Attribute <b>" + attributeName + ": </b>");
out.print(request.getAttribute(attributeName) + "<br>");

it doesn’t look like the additional attributes defined to be available to the CAS service are passed through mod_auth_cas and mod_proxy_ajp to the secured application.  We might be able to pass the data through SAML attributes but it seems that would require POST requests.

Option 2: Extend Alfresco’s Request Authn to query LDAP directly

If we can’t get the expiration date attribute from the request headers we still may be able to modify the request authentication filter to make a trip directly to the LDAP server to query for the attribute and confirm or deny authorization, but maybe we can do everything at the web server.

Option 3: Handle Authorization at Apache

The ‘auth’ in mod_auth_cas appears to only include authentication but there may be hope in allowing mod_auth_cas to handle just the authentication part then using mod_authnz_ldap or the third-party mod_authz_ldap module to handle the authorization side.

mod_authnz_ldap’s Require ldap-filter looks promising, but we would need to insert a dynamic date (today’s) for comparison to the user’s expiration date. LDAP syntax doesn’t seem to have any keyword for the current date to be handled on the server side and it doesn’t look like mod_authnz_ldap has any special tags for injecting it in the filter string so the source code would have to be modified.

mod_authz_ldap however has this in its filter configuration:

The current time in the format YYYYMMDDhhmmss

that may just do it.

Unfortunately, upon further investigation mod_authz_ldap does not support secure SSL/TLS communication with the LDAP server and hasn’t been maintained in a quite a while, so that won’t work.

Dare I try modifying the mod_authnz_ldap source to allow for a dynamic replace of a date tag?  Sure, why not?

The last time I wrote C code it was probably on a machine running Mac OS 7.6, but after several hours and as many espressos I’ve taken the relevant code from mod_authz_ldap’s source, tweaked it a bit, and found the appropriate place to inject it in mod_authnz_ldap’s authn_ldap_build_filter.

You can compile and install a single module on the server with:

apxs -i -a -c mod_authnz_ldap.c

then add the appropriate config to your location directive.  So we have CAS performing authentication and a modified mod_authnz_ldap performing authorization on our Tomcat examples app:

<Location /examples>
AuthType CAS
AuthName "CAS"
CASScope /examples
AuthLDAPURL "ldaps://,dc=company,dc=com?uid?sub?(alfrescoExpirationDate>=$tZ)"
AuthLDAPBindDN "uid=reader,ou=users,dc=company,dc=com"
AuthLDAPBindPassword "*****"
require valid-user

Again, my C chops are extremely rusty but I’ve contributed these changes to mod_authnz_ldap to Apache as Bug 47838.

Other Alfresco SSO Caveats

We can secure the Alfresco app in the same manner as /examples above but we’ll have to secure Alfresco Share with SSO as well and may run into issues with ticket parameter clashes.

As stated in one of the forum posts above, the header Alfresco needs to look for is CAS-User.  Before Alfresco 3.2 the web.xml changes would look like:

<!-- Name of HTTP header containing UserID. -->

Other Spring Apps with CAS

In some of our other apps we use Spring Security and will want to integrate them with CAS.  There’s a good write up on the details of the communication between spring security and CAS and a forum post on CAS with LDAP authorization that should help.

Hopefully this account of a mad man in pursuit of expiring authorization will be of use to someone, somewhere, someday.

Web-Based Line Chart Tools Comparison

20090901 2 comments





Google Visualization API

I’m in the process of evaluating various AJAX/DHTML frameworks for an enterprise application and one of the needs that deserved some hands-on experimentation was the ability create charts.

jQuery and YUI are in the lead as far as core frameworks for this application and the Google Visualization API seems pretty interesting so was included as well.

As a fairly simple and common use case I choose a target of a line chart that showed the number of users of a few services over time and defined some basic requirements:

  • The data must be fetched from a separate URL, not defined on the presentation page (this URL will be a web service in production)
  • Three series must be displayed at once
  • The data points should have tooltips
  • ‘Out-of-the-box’ components should be used when possible
  • A non-flash solution is preferred

Some of the points I found interesting from each framework follow. Note that the charts here are only screenshots as I didn’t find any immediately obvious way to get the real charts working on



At this time it doesn’t seem that jQuery or jQuery UI has any built-in charting abilities but there are a ton of community plugins available.

Flot looked the most promising (Sparklines also looks very good for tiny charts).


Flot seems to prefer its data in JSON format organized by series and we want to simulate a web service so we’ll create a file data/users-series-format.json containing something like:

{label: "Service 1 Users", data:[
{label: "Service 2 Users", data:[
{label: "Service 3 Users", data:[


Setup was simple enough.  Include the scripts:

<!--[if IE]><script language="javascript" type="text/javascript" src="../excanvas.pack.js"></script><![endif]-->

<script language="javascript" type="text/javascript" src="scripts/jquery/jquery-1.3.2.js"></script>

<script language="javascript" type="text/javascript" src="scripts/jquery/jquery.flot.js"></script>

put in the placeholder where you want the chart:

<div id="placeholder" style="width:400px; height:200px;"></div>

get the data and build the chart:

<script id="source" language="javascript" type="text/javascript">

$.getJSON("data/users-series-format.json", function(json){

$.plot($("#placeholder"), json, {

xaxis: { mode: "time" },

lines: { show: true },

points: { show: true }




Adding the tooltip was a little more complicated but not terribly so.



The Yahoo! User Interface Library (YUI) is a mature, robust library with Yahoo-supplied components for just about everything.

The YUI Charts Control (labeled as experimental at the time of this writing) creates nice looking charts, but they are flash-based.

There is plenty of documentation on YUI’s charts so I won’t go into too much detail but the concepts are similar to above.


YUI’s DataSource component can handle several data formats, for consistency’s sake I went with JSON so my file data/users-raw-format.json (named so since it most closely resembles the raw data used to build it) contains:

{"Response" : { "Results" : [

I did have trouble getting this data to load properly via URL when the HTML file containing the DataSource code was loaded in the browser via file:// rather than http:// even after adding the file location to the Flash global security settings.

The chart also displayed oddly when the data contained JavaScript timestamps and a date parser was used, so as you can see a string date was used in the data, not ideal but this is just proof of concept.


Include the scripts (YUI’s dependency configurator comes in handy here), add a place holder div for the chart, get the data, and build the chart.

Don’t forget to set YAHOO.widget.Chart.SWFURL to a location containing the swf.

Google Visualization API


There are some pretty slick examples in the Google’s Visualization Gallery like the Motion Chart, but for the purposes of our exploring we just need the Line Chart.

Once again we have a similar pattern for getting things running.


Google requires that the web service providing the data source implement a particular protocol and format.

We’ll again use JSON and with Google’s format our data/users-google-format.json file looks like:

{id:'s1',label:'Service 1 Users',type:'number'},
{id:'s2',label:'Service 2 Users',type:'number'},
{id:'s3',label:'Service 3 Users',type:'number'}],
{c:[{v:new Date(2009,4,7,0,0,0)},{v:110},{v:26},{v:22}]},
{c:[{v:new Date(2009,4,8,0,0,0)},{v:115},{v:31},{v:23}]}

At first the format seemed cumbersome but I realize that many users would prefer this close resemblance to how the same data would appear in a spreadsheet.


Loading of the scripts is a little different since you use Google’s core JavaScript API to load the charting tools needed and can call the chart initialization on successful load of that package:

<script type=“text/javascript” src=;></script>

<script type=“text/javascript”>

google.load(“visualization”, “1”, {packages:[“linechart”]});


where initialize loads the data:

function initialize() {

var query = new google.visualization.Query(‘data/users-google-format.json’);



and the query calls handleQueryResponse which draws the chart:

function handleQueryResponse(response) {

if (response.isError()) {

alert(‘Error in query: ‘ + response.getMessage() + ‘ ‘ + response.getDetailedMessage());



var data = response.getDataTable();

var chart = new google.visualization.LineChart(document.getElementById(‘chart_div’));

chart.draw(data, {width: 400, height: 200, is3D: true});




Even with the extensive documentation and examples available on YUI I’d have to say it was the most difficult to deal with, presenting some little problem at almost every turn.

It didn’t seem that it would be very easy to use a JSON format other than the one recommended by the framework for any of the tools evaluated, which is disappointing.

There are certainly a lot of factors to consider before choosing a UI framework, but if all I needed were line charts I’d probably hand it to Flot/jQuery.