I'd like to be able to use these "best of breed" opensource solutions, with the only requirement of some sort of single-sign-on between the different sites. I don't want my users having to log-in in 3 different places, so I though it could be possible with OpenId.
Has anyone tried something similar?
OpenID will not avoid the problem of having to sign in 3 separate times. It was allow the user to share the same login credentials between the sites, but they will have to actually log in to each of the three systems. If that is not a problem, go with OpenID. If it is, you have two options:
Use an LDAP server to authenticate on all three sites. I think all three software packages have modules/plugins for LDAP (Drupal, Moodle, MediaWiki). Once you have the LDAP server running, the rest should be easy.
Write custom modules/plugins for each platform that authenticate against a single database. Maybe you could use the Drupal database as the primary one, and have MediaWiki and Moodle authenticate with that. So, effectively, the user will only have an account on the Drupal site, but will get access to all three. This is basically the same idea as an LDAP server, but might save you some overhead and complication.
There is also the Moodle Integration module for Drupal that attempts to accomplish the same thing, only without MediaWiki in the mix. I would check that out.
Good luck!
here are three possible solutions: (1) sigle sign-in site, (2) inject login/register forms into all sites using server site includes - SSI and (3) - ajax.
Single sign-in site.
suppose you have site1.domain.com and site2.domain.com and you want to login/register at both simultaneously. Probably the easiest way to do it will be to create another domain e.g. login.domain.com that will do the job. Your login/register application will need access to databases for site1 and site2 and/or their api's. Since login status usually resides in the cookies, your login application will need to set those login cookies to both sites simultaneously (on successful login/registration) and delete on logout.
To set cookies for all sites from login.domain.com - all of the must sit on .domain.com and cookie domain parameter must be .domain.com
If your solution needs both api access (to the other applications) and access to the same database by several applications - you may need to deal with database transactions. This is because new registrations won't be visible on other sites until transaction is committed - so for example - you can not call api from within login code to retrieve cookies before committing the transaction with the new registration.
One important detail. If you already have users separately registered at site1 and/or site2 but not on both your signon site will either have to handle those cases or you'll need to sync registrations manually yourself upon deployment of your new registration system. Manual fix won't be possible when extra user input is required to complete the cross-site registration. This point also becomes important when you add new sites requiring some new user input for the registration.
Finally, carefully choose domain name handling OpenID. To the best of my knowledge it is impossible to transfer openid endorsements across subdomains without users consent - please correct me if I am wrong. You don't want to ask users to re-register just because you decide to rename the sub-domain.
server side include (ssi) method
Another solution is to inject those forms via sever-side includes into all sites. This may be considerably harder and will depend on the type of webserver in use and will work slower.
A pre-requisite here is that all your applications run on the same subdomain - so that openid works for all of them.
I've once built common user registration for MW (php) and cnprog (python/django).
My solution was to display the same exact registration form on the wiki and the forum site, while generating and processing this form with django. I did it this way because wiki and forum "skins" are so different that I did not want to surprise visitors with the dramatic change of site appearance when they go to the registration page. This is complicated and I will not do it again :) and instead would go with single sign-in method.
in order to display django output through mediawiki I've created a wiki extension printing apache "include virtual" call to glue django-generated content with the wiki output. This comes with problems.
Apache include virtual on my installation cannot POST to subrequests and cannot pass cookies from subrequests and cannot pass redirect responses (all http headers will be thrown out) to the upstream user requests.
So I've added "was_posted=true" to mark the posts for django and a secret code to prevent cross-site forgery. To get the cookies out - had them printed with cookie_morsel.output_js() in python. So javascript must run on the client for this to work. Any redirects will have to be done with javascript too. Extra work will still be needed to upload files (like avatar picture).
So single sign-on may be the best solution.
ajax may be a neat way around - just build forms in all of your sites with javascript and submit them via ajax. Will work fast and will not break appearance of your various sites, but this won't please the folks allergic to javascript.
Actually, the only method that does not require any javascript is single sign-in site.
Posted this because I've spent enough time building this thing for MW and django - an hour of typing did not make a difference :).