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A draft of this document prompted the question

"Why does an instance of a LoginController need to support more than one type of Credentials?"

Any given CAS deployment might want to support more than one type of credentials. Say, username/password and also desktop Kerberos. So we'd have two radically different kinds of Credentials.

One way to handle this would be to have multiple instances of the LoginController, one for each type of credentials we might handle. But how did we know which LoginController to go to? We probably shouldn't switch on the URL, since after all any given CAS client is going to redirect to the single institutional CAS login URL regardless of end user preference about what kind of credential she wants to present.

Another way (I propose) is to give our LoginController a plugin, a RequestToCredentials. This object is responsible for examining the HttpServletRequest and returning the Credentials it represents. It is these credentials that get passed from LoginController into the CentralAuthenticationService for processing.

One plausible implementation of this interface will be the implementation that delegates to a List of other implementations, returning true to supports() if any of its children support the presented HttpServletRequest and returning the Credentials returned by the first of its children to support the request.

/**
 * Interface for components that know how to extract from HttpServletRequest
 * whatever it is that constitutes actual arguments of the request for authentication.
 */
public interface RequestToCredentials {

    /**
     * Parse an HttpServletRequest and extract from it whatever it is that is necessary as input to the AuthenticationHandler
     * which will examine the request for authentication represented by the HttpServletRequest. Return an Object
     * encapsulating that extracted information.  Specific implementations will return specific objects which in turn specific
     * AuthenticationHandler implementations will expect and consume.
     * @returns an object representing the relevant information for the authentication request
     * @throws RuntimeException - indicates failure
     */
   booleanObject supportscredentialsFromHttpServletRequest(HttpServletRequest httpServletRequest);

 }

protected Object getCommand(HttpServletRequest request) throws Exception {
    return createCommand();
}

protected Object getCommand(HttpServletRequest request) throws Exception {
    return this.requestToCredentials.credentialsFromHttpServletRequest(request);
}

protected final Object getCommand(HttpServletRequest request) throws Exception {
    if (!isSessionForm()) {
        return formBackingObject(request);
    }
    HttpSession session = request.getSession(false);
        if (session == null) {
            throw new ServletException("Must have session when trying to bind");
        }
        Object formObject = session.getAttribute(getFormSessionAttributeName());
        session.removeAttribute(getFormSessionAttributeName());
        if (formObject == null) {
            throw new ServletException("Form object not found in session");
        }
    return formObject;
}

protected Object formBackingObject(HttpServletRequest request) throws Exception {
    return createCommand();
}

    protected ModelAndView processFormSubmission(final HttpServletRequest request, final HttpServletResponse response, final Object object,
        final BindException errors) throws Exception {
        final Credentials credentials = (Credentials)object;
       protected ModelAndView
processFormSubmission(final HttpServletRequest request, final HttpServletResponse response, final Object object, this.credentialsBinder.bind(request, credentials);

        final BindExceptionString errors)ticketGrantingTicketId throws Exception {= this.centralAuthenticationService.createTicketGrantingTicket(credentials);
         final CredentialsString credentialsservice = (Credentials)objectrequest.getParameter(WebConstants.SERVICE);
        final boolean warn = StringUtils.hasText(request.getParameter(WebConstants.WARN));

public  this.credentialsBinder.bind(request, credentials);class LoginForm {
    private String service;
  final String ticketGrantingTicketIdprivate = this.centralAuthenticationService.createTicketGrantingTicket(credentials)boolean warn;
    
   final /** String
service = request.getParameter(WebConstants.SERVICE);   * Set the Service to which finalthe booleanrequestor warnseeks =to StringUtils.hasText(request.getParameter(WebConstants.WARN));

public class LoginForm {authenticate.
     */
    public privatevoid setService(String service;) {
        privatethis.service boolean= warnservice;
    }

    /**
      * Set whether the user Servicewould like to be warned whichupon theSingle requestorSign seeksOn to subsequent authenticateservices.
     */
    public void setServicesetWarn(Stringboolean service) {
   warn) {
        this.warn = warn;
    }

 ... and corresponding getters

}

 

 protected this.service = service;
    }

ModelAndView processFormSubmission(final HttpServletRequest request, final HttpServletResponse response, final Object object,
   /**     final *BindException Seterrors) whetherthrows theException user{
would like to be warned upon Single Sign Onfinal toLoginForm subsequentloginForm services.= (LoginForm) object;
   */     public
void setWarn(boolean warn) {     final Object credentials = this.warn = warn;requestToCredentials.credentialsFromHttpServletRequest(request);

     }   ...final andString correspondingticketGrantingTicketId getters

}= this.centralAuthenticationService.createTicketGrantingTicket(credentials);