Example authentication driver for Laravel 4.

AuthUserProvider.php

<?php namespace Project\Providers;

use Illuminate\Auth\UserProviderInterface;
use Illuminate\Auth\GenericUser;

class AuthUserProvider implements UserProviderInterface {

	/**
	* External webservice for authentication
	*/
	private $webservice;


	/**
	* The user object.
	*/
	private $user;


	/**
	* Constructor
	*
	* @return void
	*/
	public function __construct(\Project\Webservice\Auth $webservice)
	{
	    $this->webservice = $webservice;
	    $this->user = null;
	}


	/**
	* Retrieves a user by id
	*
	* @param int $identifier
	* @return mixed null|array
	*/
	public function retrieveByID($identifier)
	{
	    $this->user = is_null($this->user) ? $this->webservice->find($identifier) : $this->user;
	    return $this->user;
	}
	

	/**
	* Tries to find a user based on the credentials passed.
	*
	* @param array $crendtials username|password
	* @return mixed bool|UserInterface
	*/
	public function retrieveByCredentials(array $credentials)
	{
	    if(!$user = $this->webservice->find($credentials['username'])) return false;

	    return new GenericUser($user);
	}


	/**
	* Validates the credentials passed to the ones in webservice.
	*
	* @param UserInterface $user
	* @param array $credentials
	* @return bool
	*/
	public function validateCredentials(\Illuminate\Auth\UserInterface $user, array $credentials)
	{
		return $this->webservice->validateCredentials($credentials['password'], $user->password);
	}
}

Should be $this->webservice in last method...

@helmut: You are absolutely correct. Thanks, fixed it now.

Thanks for the code!
Just a late edit - retrieveByCredentials should return null instead of false on line 53

Thanks for you tutorial, but I still don't get what is your $webservice variable. What does it mean? Can you show an example of it, please?