Authentication Initiation

Authentication processing is currently implemented using the following components:

• The SlingAuthenticator class is managed by the SlingMainServlet and is used as a backend for the OSGi HttpContext.handleSecurity method.
• The AuthenticationHandler interface is a service interface, which may be used to extend authentication protocols. Currently Sling includes two implementations of this interface for the standard HTTP Basic authentication and for OpenID authentication.
• To initiate a login one or more servlets or scripts have to be written, which create requests suitable for authentication. For example the LoginServlet of the org.apache.sling.httpauth bundle uses an HTML form and Ajax requests to setup the HTTP BASIC authentication.
• The HTTP Basic authentication handler supports a sling:authRequestLogin parameter to have a client request ask for authentication.

This approach currently has two major issues:

1. Initiating authentication can only be done by the user requesting the login servlet or script. For example to initiate HTTP Basic authentication using the org.apache.sling.httpauth bundle, the user has to actively request the /system/sling/login.html page.
2. There is a conceptual break between login initiation (or form rendering) and authentication handling.
3. The sling:authRequestLogin parameter is only obeyed if HTTP Basic authentication is used and the handler is deemed responsible for the request.

To solve these issues, I suggest we add a new API, which may be used to force the initiation of authentication from servlets or scripts. This new API would be implemented such, that a AuthenticationHandler is selected based on some path (just like for the actual authentication) and the AuthenticationHandler.requestAuthentication method is called.

Currently the AuthenticationHandler.requestAuthentication method is only called if an authentication request, which has been initiated from the client side for example by submitting a form, failed and must be reissued. With the new approach, this method may also be called to initiate authentication.

API extension

A new Authenticator interface is defined and exported in the org.apache.sling.engine bundle :

/**
 * The <code>Authenticator</code> interface defines the service interface of the
 * authenticator used by the Sling engine. This service provides a method to
 * find an {@link AuthenticationHandler} and call its
 * {@link AuthenticationHandler#requestAuthentication(HttpServletRequest, HttpServletResponse)}
 * method.
 * <p>
 * This interface is not intended to be implemented by applications but may be
 * used to initiate the authentication process form a request processing servlet
 * or script.
 * 
 * @since 2.0.4
 */
public interface Authenticator {

    /**
     * Finds an {@link AuthenticationHandler} for the given request and call its
     * {@link AuthenticationHandler#requestAuthentication(HttpServletRequest, HttpServletResponse)}
     * method to initiate an authentication process with the client.
     * <p>
     * This method must be called on an uncommitted response since the
     * implementation may want to reset the response to start the authentication
     * process with a clean response. If the response is already committed an
     * <code>IllegalStateException</code> is thrown.
     * <p>
     * After this method has finished, request processing should be terminated
     * and the response be considered committed and finished.
     * 
     * @param request The object representing the client request.
     * @param response The object representing the response to the client.
     * @throws IllegalStateException If the response has already been committed.
     */
    public void requestAuthentication(HttpServletRequest request,
            HttpServletResponse response);

}

This interface is implemented by the SlingAuthenticator class which is also registered under this service interface. The SlingAuthenticator implementation in fact already has an implementation of this method, which finds an AuthenticationHandler for the request and calls its requestAuthentication method.

Generalize sling:authRequestLogin

The request parameter sling:authRequestLogin should be generalized and supported by the SlingAuthenticator: If none of the registered authentication handlers is able to extract credentials this parameter should cause the authenticator to call Authenticator.requestAuthentication method to initiate a login process.

HTTP Basic Authentication Changes

The implementation of the HTTP Basic Authentication bundle org.apache.sling.httpauth is modified as follows:

• The AuthorizationHeaderAuthenticationHandler is modified to render the login form when the requestAuthentication method is called.
• The LoginServlet is modified to just call the Authenticator.requestAuthentication method instead of rendering the form itself.