This is a Slim middleware that provides http basic authentication.

HttpBasicAuth.php

<?php
/**
 * This is a Slim middleware that provides http basic authentication.
 *
 * usage:
 * 
 *   $app->add(new HttpBasicAuth(array(
 *       'users' => array('username' => 'password'),
 *       'when' => function(\Slim\Http\Request $req, $res){
 *         return $req->getPathInfo() === '/admin';
 *       }
 *   )));
 *
 * Ref. http://www.9bitstudios.com/2013/06/basic-http-authentication-with-the-slim-php-framework-rest-api/
 */

class HttpBasicAuth extends \Slim\Middleware
{
    /**
     * @var array
     */
    protected $options;
 
    /**
     * Constructor
     *
     * @param   string  $options      The HTTP Authentication realm
     */
    public function __construct($options = array())
    {
        $defaults = array('realm' => 'Protected Area');
        if (is_string($options)){
          $options = array('realm' => $options);
        }
        $options = array_merge($defaults, $options);
        
        $this->options = $options;
    }
 
    /**
     * Deny Access
     *
     */   
    public function deny_access() {
        $res = $this->app->response();
        $res->status(401);
        $res->header('WWW-Authenticate', sprintf('Basic realm="%s"', $this->options['realm']));        
    }
 
    /**
     * Authenticate 
     *
     * @param   string  $username   The HTTP Authentication username
     * @param   string  $password   The HTTP Authentication password     
     *
     */
    public function authenticate($username, $password) {
        if(!ctype_alnum($username))
            return false;
         
        if(isset($username) && isset($password)) {
            $users = $this->options['users'];
            
            if (isset($users[$username])){
                if ($users[$username] === $password){
                    return true;
                }
            }
            return false;
        }
        else
            return false;
    }
 
    /**
     * Call
     *
     * This method will check the HTTP request headers for previous authentication. If
     * the request has already authenticated, the next middleware is called. Otherwise,
     * a 401 Authentication Required response is returned to the client.
     */
    public function call()
    {
        $req = $this->app->request();
        $res = $this->app->response();
        
        if (isset($this->options['when']) && is_callable($this->options['when'])){
            if (false === call_user_func_array($this->options['when'], array($req, $res))){
                return $this->next->call();
            }
        }
        
        $authUser = $req->headers('PHP_AUTH_USER');
        $authPass = $req->headers('PHP_AUTH_PW');
        
        if ($this->authenticate($authUser, $authPass)) {
            $this->next->call();
        } else {
            $this->deny_access();
        }
    }
}