[The 'and a half' option was Liberty Alliance / SAML 2 Authentication Plugin for PAS. I'm discounting it for the time being because a) it doesn't look as if it will work with Shib 3, b) there hasn't been a release since December 2008, and c) the most recent release gives '404 Not found' on the Plone web site]
The two remaining options were WebServerAuth and a set of products from Ithaka (AutoUserMakerPASPlugin, ShibbolethLogin, ShibbolethPermissions). They have quite a lot in common (which is not surprising since they share a common ancestor).
- Both depend on the Apache Shibboleth module to perform authentication, and so require connections to Plone to be proxied through Apache.
- For this to work, server variables provided by the Shib module have to be converted to headers in the proxied request - doing so is a matter of Apache configuration. It is important to ensure that unauthenticated users can't spoof any such headers used for anything related to security.
- Both will allow Plone access by anyone who can successfully authenticate - if this isn't appropriate then Apache access controls could be used to limit this further (and WebServerAuth has an additional option).
- Both require a unique user identifier. Easiest to use the value in REMOTE_USER which is set by default by the Shib module to the first non-blank value in eduPersonPrincipleName or the SAML 2 or SAML1 versions of eduPersonTargetedID. This leads to some unwieldy userIDs - both products can strip domain names from IDs, but this removes any guarantee of uniqueness.
- Both force authentication for an https: version of the site while allowing unauthenticated access to the http: version. While Shib's 'Lazy Session' features might make this unnecessary, both products will in principle work with other webserver-based authentication schemes that may not support anything similar.
- For both, it's advisable to suppress the default 'login' portlet that is displayed to unauthenticated users.
- WebServerAuth doesn't create users in the database - by default they just get assigned the 'Authenticated' role (not 'Member') when they log in. It uses userID (so eduPersonPrincipleName or eduPersonTargetedID, optionally with domains stripped) as the user's Full Name - it doesn't use any other Shib attributes even if they are available.
- Users requiring additional rights can be created in the Plone database and appropriate rights will be assigned when the corresponding users authenticate. Creating Plone users with IDs containing '@' and '.' requires a long-winded hack.
- WebServerAuth can be configured only to authenticate users who have corresponding Plone accounts, but the user interface is sub-optimal: people will log in and apparently succeed, only to be greeted with a Plone page that still has a "Log In" link.
- By default, WebServerAuth redirects to the https: version of the current page when authentication is required (and modifies the standard 'log in' link to achieve this). This will cause the Apache module's default Sessioninitiator to be used for authentication. Optionally WebServerAuth can redirect to a customised URL which could perhaps be used to implement a local WAYF service (e.g. simplified login for local users; redirect to federation WAYF for others). Essentially WebServerAuth takes over all login access to the site (which can be problematic if it fails...).
- WebServerAuth is under current development - its author contacted me within hours of my posting my earlier article to point out an error with it.
- Need to set the standard logout link (ZMI --> Plone --> postal_actions --> user --> logout --> URL) to something apropriate (or perhaps suppress the link altogether?)
- AutoUserMakerPASPlugin creates real Plone users as new people authenticate. It can use configurable Shib attributes to initialise full name, email, location, roles and group membership. This only applies to user creation - once created, changes to attributes are not propagated and the users need to be managed on Plone. It seems necessary to configure full name to fall back to userID if nothing else is available to avoid all such users ending up with a full name of '(null)'.
- AutoUserMakerPASPlugin can be configured to strip either all or selected domains from userIDs - one approach might be to strip just a local domain, giving local users short userIDs while ensuring against name clashes with anyone else.
- AutoUserMakerPASPlugin supports a configurable 'logout' URL that can invoke the local Shib module logout function. This may be confusing in a wider single sign-on context (but is handy for testing).
- ShibbolethPermisisons adds the ability to add local (per page or per container) access rights based on configurable Shib attributes. Again, this only applies at account creation time, after which rights have to be managed manually within Plone as usual.
- ShibbolethLogin installs a replacement for the standard login page. This includes configurable links either to local SessionInitiator URLs or direct to Shib 1 IdPs or WAYFs. So for example it's possible to have a 'Log in with a Raven (University of Cambridge) user id' link for local users and a more general 'Log in with a different UK Federation user id' link for everyone else. Local Plone user authentication (with username/password) remains available. ShibbolethLogin appears to be targeted at Shib 1 functionality, with no obvious support for new Shib 2 functionality, such as the Discovery Service.
- The maintenance status to the Ithica products is unclear. Documentation reports the most recent tests to have been with "Zope 2.10.5 and Plone 3.0.6"; files in the distribution appear to have been modified most recently in May 2008.