My solution was to use token login to handle the actual request. The process is a tad convoluted, but the diagram should explain how the system works:

So the user logs into a remote service, which proxies a username to the Joomla! which is picked up by SSO HTTP in a custom component which generates a token using the detected username, redirects the user to the token login component (not through the proxy) which then lets the user log in and continue through the site.

So what we need to create is a new component to handle detecting the user, creating the token and them redirecting them. We can use the SSO HTTP plugin to handle detecting the remote user perfectly fine (this has already been tested) and the Token Login component can handle validating tokens and redirecting users.

Step 1: Prerequisites
I’m going to use the JAuthTools packages available from Joomla!Code. To install these, you will need to install the Advanced Tools package first before you get started. The latest version is Advanced Tools 1.5.1 available from JoomlaCode.

Once we’ve got the Advanced Tools installed, we’re going to need the JAuthTools 1.5.4 Core package. This will give us the SSO library that we’re going to use later on. We will also need the SSO plugins package (for the SSO HTTP plugin in our case) and the Token Login package. As we’re not using the user source plugins for this case (both LDAP and Session are provided by default) we don’t need to install them and since we’re going to write our own SSO detection component we don’t need to use the options offered by the SSO package.

Once we’ve got all of the prerequisites installed we can start building the component

Step 2: Building the component
So we’ll start building our component with the basic few lines all components require:

This basic check ensures that we’re within Joomla!’s confines or kills the execution if we’re not. From here, lets set up some basic variables:

These are two variables we’re going to use later. The landing page is used for token login to redirect the user to a page once they’ve been authenticated successfully. The autocreate option is utilised by the SSO system to determine if it should automatically create the user. Keep these in mind as we’ll use them later on.

In this next phase we’re going to take a copy of the current user and then use the SSO system to attempt to do the login. If its successful, the user’s ID will change and we can then create a token for them and redirect so they can login, if not we’ll redirect them with an error message:

So we get a reference to the user object, get a copy of the user ID, import the SSO library, create a new SSO authentication object and handle authentication. We see the $autocreate variable we initialised before used here. We could load the plugins ourselves and handle everything but the doSSOAuth call will handle this for us, create the users session and if requested attempt to create the user if they don’t exist. We can then check if the user ID’s are different and then create a token to direct the user back:

A sizable chunk of code. So we check if the user ID has changed (typically from unauthenticated to authenticated, we could also just check if the user ID != 0 as well). We then import the token login library, grab a copy of the database object and then create a new token.

So with the token, we set the username to be that of the currently authenticated user (which we know is correct), set the expiry to be the present time plus an hour. Since this data is only ‘temporary’ we don’t bother with JDate and just use the server time. If the server transitions to or from daylight savings there could be an issue but since the user should be redirected rather quickly that seems like an unlikely possibility. We set the number of logins that the token is valid for, which for this case is only one and then we set the token’s landing page to be the value of $landingpage that we set before. Once we’ve set all of the data we call the ‘store’ function to save all of this to the database which will also trigger the generation of the login token.

Since the session we’re currently in is invalid, we destroy it for a bit of extra security and then we redirect the user to the token login component. Since this request will get proxied as a redirect to the real site (hopefully the proxy doesn’t rewrite the redirect header coming back otherwise this will fail), token login can then authenticate the user (again) and create a session for them without the proxies’ interference. There is however one last part of our component, which is the else case for if the user doesn’t get detected:

So if we don’t detect anything, redirect the user to index.php with the message ‘Invalid SSO Request’. Too easy almost!

So for reference below is the final completed component file, don’t forget to update the values of $landingpage and $autocreate: