Symfony 2: access to a firewall with two separate providers

We have a system in which administrators and standard users are processed by individual security providers. This caused a problem on the administration pages because administrators cannot access the files or images located behind the firewall of the main site unless they are also logged in to the main site.

Images and files must be accessible to all authenticated users and administrators, regardless of provider. They are served through a controller that provides more precise access control.

Is it possible to define more than one provider to allow access to the route?

Here is a stripped down version of our current security.yml:

security:
    providers:
        admin_user_db:
            entity: { class: OurAdminUserBundle:AdminUser, property: username }
        site_user_db:
            entity: { class: OurSiteUserBundle:SiteUser, property: username }
    firewalls:
        admin_login:
            pattern:  ^/admin/login$
            security: false
        site_user_login:
            pattern: ^/login
            security: false
        file_route:
            pattern: ^/file
            anonymous: ~
            ### We need to allow this route only for authorized users from
            ### either admin_user_db or site_user_db providers
        admin_secured_area:
            pattern: ^/admin
            http_basic: ~
            provider: admin_user_db
            form_login:
                check_path: /admin/login_check
                login_path: /admin/login
            logout:
                path:   /admin/logout
                target: /
        site_secured_area:
            pattern: .*
            http_basic: ~
            provider: site_user_db
            form_login:
                check_path: /check_login
                login_path: /login
                failure_path: /login
                failure_forward: false
            logout:
                path:   /logout
                target: /