$ldapserver = 'server.ip.address';
$ldapuser = '_user_for_search_sAMAccountname';
$ldappass = '_user_pass';
$ldapconn = ldap_connect($ldapserver);
if($ldapconn) {
    $ldapbind = ldap_bind($ldapconn, $ldapuser, $ldappass);
    if ($ldapbind) echo "LDAP bind successful...n";
}

services:
    app.ldap:
        class: SymfonyComponentLdapLdapClient
        arguments: [ "server.ip.address" ]

security:
    role_hierarchy:
        ROLE_ADMIN: [ROLE_USER]
    providers:
        app_users:
            ldap:
                service: app.ldap
                base_dn: ou=staff,dc=ldap,dc=server,dc=com
                search_dn: _user_for_search_sAMAccountname
                search_password: _user_pass
                filter: "(sAMAccountName={username})"
                default_roles: ROLE_USER

    firewalls:
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false
        main:
            provider: app_users
            pattern:  ^/
            logout:
                path:   /logout
                target: /
            form_login_ldap:
                service: app.ldap
                dn_string: "{username}" # !!! differs from default but no luck
                check_path: /login_check
                login_path: /login
            security: true
            anonymous: true
    access_control:
        - { path: /login, roles: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: /user, roles: ROLE_USER }
        - { path: /.*, roles: IS_AUTHENTICATED_ANONYMOUSLY }

login:
    path: /login
    defaults: { _controller: R61IP4BillBundle:Security:login }

login_check:
    path: /login_check

logout:
    path: /logout

user:
    path: /user
    defaults: { _controller: R61IP4BillBundle:Default:user }

class SecurityController extends Controller
{
    public function loginAction(Request $request)
    {
        $authenticationUtils = $this->get('security.authentication_utils');
        $error = $authenticationUtils->getLastAuthenticationError();

        return $this->render(
            'R61IP4BillBundle:Security:login.html.twig',
            array(
                'error' => $error,
            )
        );
    }
}

{% if error %}
    <div>{{ error.messageKey|trans(error.messageData, 'security') }}</div>
{% endif %}
<form action="{{ path('login') }}" method="post">
    <label for="username">Username:</label>
    <input type="text" id="username" name="_username" />

    <label for="password">Password:</label>
    <input type="password" id="password" name="_password" />

    {#
        If you want to control the URL the user
        is redirected to on success (more details below)
        <input type="hidden" name="_target_path" value="/account" />
    #}
    <button type="submit">login</button>
</form>