Authentication

Elgg provides everything needed to authenticate users via username/email and password out of the box, including:

remember-me cookies for persistent login

password reset logic

secure storage of passwords

logout

UIs for accomplishing all of the above

All that’s left for you to do as a developer is to use the built-in authentication functions to secure your pages and actions.

Working with the logged in user

Check whether the current user is logged in with elgg_is_logged_in():

if (elgg_is_logged_in()) {
  // do something just for logged-in users
}

Check if the current user is an admin with elgg_is_admin_logged_in():

if (elgg_is_admin_logged_in()) {
  // do something just for admins
}

Get the currently logged in user with elgg_get_logged_in_user_entity():

$user = elgg_get_logged_in_user_entity();

The returned object is an ElggUser so you can use all the methods and properties of that class to access information about the user. If the user is not logged in, this will return null, so be sure to check for that first.

Gatekeepers

Gatekeeper functions allow you to manage how code gets executed by applying access control rules.

Forward a user to the front page if they are not logged in with elgg_gatekeeper():

elgg_gatekeeper();

echo "Information for logged-in users only";

Forward a user to the front page unless they are an admin with elgg_admin_gatekeeper():

elgg_admin_gatekeeper();

echo "Information for admins only";

Pluggable Authentication Modules

Elgg has support for Pluggable Authentication Modules (PAM), which enables you to write your own authentication handlers. Whenever a request needs to get authenticated the system will call elgg_pam_authenticate() which probes the registered PAM handlers until one returns success.

The preferred approach is to create a separate Elgg plugin which will have one simple task: to process an authentication request. This involves setting up an authentication handler in the plugin’s Bootstrap class, and to register it with the PAM module so it will get processed whenever the system needs to authenticate a request.

The authentication handler is a function and takes a single parameter. Registering the handler is being done by elgg_register_pam_handler() which takes the name of the authentication handler, the importance and the policy as parameters. It is advised to register the handler in the plugin’s init function, for example:

// classes/Your/Plugin/Bootstrap.php

function init() {
   // Register the authentication handler
   elgg_register_pam_handler('your_plugin_auth_handler');
}

// your_plugin/lib/functions.php

function your_plugin_auth_handler($credentials) {
   // do things ...
}

Importance

By default an authentication module is registered with an importance of sufficient.

In a list of authentication modules; if any one marked sufficient returns true, elgg_pam_authenticate() will also return true. The exception to this is when an authentication module is registered with an importance of required. All required modules must return true for elgg_pam_authenticate() to return true, regardless of whether all sufficient modules return true.

Passed credentials

The format of the credentials passed to the handler can vary, depending on the originating request. For example, a regular login via the login form will create a named array, with the keys username and password. If a request was made for example via XML-RPC then the credentials will be set in the HTTP header, so in this case nothing will get passed to the authentication handler and the handler will need to perform steps on its own to authenticate the request.

Return value

The authentication handle should return a boolean, indicating if the request could be authenticated or not. One caveat is that in case of a regular user login where credentials are available as username and password the user will get logged in. In case of the XML-RPC example the authentication handler will need to perform this step itself since the rest of the system will not have any idea of either possible formats of credentials passed nor its contents. Logging in a user is quite simple and is being done by elgg_login(), which expects an ElggUser object.