SEC-977: CAS gateway feature support

[spring-projects-issues]

Martin Buechler(Migrated from SEC-977) said:

Acegi CAS client integration should also allow CAS gateway calls for configurable entry points like home/welcome/landing pages:
Reference: http://www.ja-sig.org/products/cas/client/gateway/index.html, and http://thread.gmane.org/gmane.comp.java.jasig.cas.user/32 from 2006!

[spring-projects-issues]

Rob Winch said:

I am also interested in this issue and would be willing to contribute. Can anyone point me to the process for providing a contribution?

Thanks,
Rob

[spring-projects-issues]

Martin Buechler said:

great: it works
not so great: no single configuration option, no tests

gateway.patch:
- based on http://acegisecurity.svn.sourceforge.net/svnroot/acegisecurity/spring-security/tags/release_1_0_4
- hacked necessary steps for CAS 3 Gateway feature into
core/src/main/java/org/acegisecurity/intercept/AbstractSecurityInterceptor.java
core/src/main/java/org/acegisecurity/providers/cas/CasAuthenticationProvider.java
core/src/main/java/org/acegisecurity/providers/cas/CasGatewayAuthenticationException.java (NEW)
core/src/main/java/org/acegisecurity/ui/AbstractProcessingFilter.java
core/src/main/java/org/acegisecurity/ui/cas/CasProcessingFilterEntryPoint.java
core/src/main/java/org/acegisecurity/ui/cas/ServiceProperties.java

securityContext.xml.diff
- based on example from CAS3 webapp: https://www.ja-sig.org/svn/cas3/tags/cas-3-1-0-final/cas-server-webapp/src/main/webapp/WEB-INF/securityContext.xml
- you’ll see: 3 times same config option for acegi spring beans, since functionality is spread all over the place… by design ;)

comments?
please review

[spring-projects-issues]

Luke Taylor said:

Any comments, Scott?

[spring-projects-issues]

Jeremy said:

Looking in the forums and other sites, it seems like there is a big need for this feature. Has there been any progress made for adding gateway support?

[spring-projects-issues]

Jeremy said:

Sorry, I forgot to add that I found this possible solution. Thoughts?

http://prodia.co.uk/blog/doahh/entry/spring_cas_with_unprotected_pages

[spring-projects-issues]

Tim Lenz said:

I also took a stab at a custom filter for gateway authentication, and tried to simplify a lot of the things in the solution posted above. My solution depends on a second, custom implementation of CasAuthenticationEntryPoint in which the "gateway" parameter is always set to true. I did this by overriding the createRedirectUrl() method. The filter itself does three important things

(1) If the user is already signed in or gateway authentication was already attempted, continue with the filter chain, otherwise
(2) Save the request in a requestCache so that either the AuthenticationSuccessHandler or AuthenticationFailureHandler will know where to go after receiving the response back from CAS
(3) redirect to CAS for gateway authentication

Your AuthenticationFailureHandler then just needs to check whether gateway authentication was attempted, and if so, redirect the user to the URL in the saved request. I think the only disadvantage to this approach is that it requires sessions for every page in your application. However, you might be able to work around this with a cookie implementation.

public class CasUnprotectedPageFilter extends GenericFilterBean
{
    private static final Logger logger = Logger.getLogger(CasUnprotectedPageFilter.class);

    private RequestCache requestCache = new HttpSessionRequestCache();

    //Assumed to be a custom implementation where useGateway is always set to TRUE
    private CasAuthenticationEntryPoint casAuthenticationEntryPoint;

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException 
    {
        if (User.isLoggedIn())
        {   //If we're already logged in, there's no work to do
            chain.doFilter(req,res);
            return;
        }

        HttpServletRequest request = (HttpServletRequest) req;  
        boolean attemptedGatewayAuth = WebUtils.getSessionAttribute(request,"ATTEMPTED_GATEWAY_AUTH") != null;        
        if(!attemptedGatewayAuth)
        {           
            request.getSession().setAttribute("ATTEMPTED_GATEWAY_AUTH",true);

            HttpServletResponse response = (HttpServletResponse) res;

            //Save the request so either the AuthenticationSuccessHandler or AuthenticationFailureHandler will know where to go after receiving the response back from CAS
            requestCache.saveRequest(request, response);

            //Try to authenticate with CAS gateway. Not entirely sure why we're passing in an exception to this method
            if (logger.isDebugEnabled())
                logger.debug("Commencing CAS gateway authentication");

            casAuthenticationEntryPoint.commence(request,response,new AuthenticationCredentialsNotFoundException("Authentication credentials not found"));

            //Skip the rest of the filter chain
            return;
        }

        //Already tried gateway authentication and not logged in, continue with filter chain        
        chain.doFilter(req,res);                            
    }    

    public void setGatewayEnabledCasAuthenticationEntryPoint(
            CasAuthenticationEntryPoint casAuthenticationEntryPoint) {
        this.casAuthenticationEntryPoint = casAuthenticationEntryPoint;
    }
}

public class GatewayAwareAuthenticationFailureHandler implements AuthenticationFailureHandler 
{
    private RequestCache requestCache = new HttpSessionRequestCache();
    private RedirectStrategy redirectStrategy = new DefaultRedirectStrategy();

    //Used as a fallback for when gateway authentication was not attempted
    private AuthenticationFailureHandler authenticationFailureHandler = new SimpleUrlAuthenticationFailureHandler();

    public void onAuthenticationFailure(HttpServletRequest request,
            HttpServletResponse response, AuthenticationException exception)
            throws IOException, ServletException 
    {   
        boolean attemptedGatewayAuth = WebUtils.getSessionAttribute(request,"ATTEMPTED_GATEWAY_AUTH") != null;
        if (attemptedGatewayAuth)
        {
            //Invalid ticket, or no ticket received from CAS gateway--should have a SavedRequest in the session for the unprotected page
            SavedRequest savedRequest = requestCache.getRequest(request, response);
            if (savedRequest != null)
            {
                String targetUrl = savedRequest.getRedirectUrl();          
                redirectStrategy.sendRedirect(request, response, targetUrl);
                return;
            }
        }

        authenticationFailureHandler.onAuthenticationFailure(request, response, exception);     
    }

    public void setRequestCache(RequestCache requestCache) {
        this.requestCache = requestCache;
    }

    public void setFallbackAuthenticationFailureHandler(
            AuthenticationFailureHandler authenticationFailureHandler) {
        this.authenticationFailureHandler = authenticationFailureHandler;
    }
}

[spring-projects-issues]

Eduard Gurskiy said:

Tim, thanks for this solution! Could you clarify how is it possible to configure such "gateway" behavior for some specific URLs in my app using "intercept-url" patterns?

[spring-projects-issues]

Tim Lenz said:

Good question! After my original post, I realized there were certain unprotected URLs that I didn't want to gateway at all (mostly AJAX services). Here's a new version of the filter that supports a list of "doNotGateway" expressions. It could probably be easily modified to support the reverse, i.e. a specific list of URLs to gateway.

public class CasUnprotectedPageFilter extends GenericFilterBean
{
    private static final Logger logger = Logger.getLogger(CasUnprotectedPageFilter.class);

    private RequestCache requestCache = new HttpSessionRequestCache();

    /**
     * A list of regular expressions the filter should NOT gateway to CAS
     */
    private List<RegexRequestMatcher> doNotGateway = new ArrayList<RegexRequestMatcher>();

    //Assumed to be a custom implementation where useGateway is always set to TRUE
    private CasAuthenticationEntryPoint casAuthenticationEntryPoint;

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException 
    {
        //If we're already logged in, there's no work to do
        if (CasUser.isLoggedIn())
        {   
            chain.doFilter(req,res);
            return;
        }

        HttpServletRequest request = (HttpServletRequest) req;
        boolean attemptedGatewayAuth = WebUtils.getSessionAttribute(request,"ATTEMPTED_GATEWAY_AUTH") != null;      
        if (attemptedGatewayAuth)
        {   //Already tried gateway authentication and not logged in, continue with filter chain 
            chain.doFilter(req,res);
            return;
        }

        //Compare request with doNotGateway patterns
        for (RegexRequestMatcher rrm:doNotGateway)
        {  
            if (rrm.matches(request))
            {
                //Exit filter if we find a match
                chain.doFilter(req,res);
                return;
            }
        }       

        request.getSession().setAttribute("ATTEMPTED_GATEWAY_AUTH",true);

        HttpServletResponse response = (HttpServletResponse) res;

        //Save the request so either the AuthenticationSuccessHandler or AuthenticationFailureHandler will know where to go after receiving the response back from CAS
        requestCache.saveRequest(request, response);

        //Try to authenticate with CAS gateway. Not entirely sure why we're passing in an exception to this method
        if (logger.isDebugEnabled())
            logger.debug("Commencing CAS gateway authentication");

        casAuthenticationEntryPoint.commence(request,response,new AuthenticationCredentialsNotFoundException("Authentication credentials not found"));

        return;
    }    

    public void setGatewayEnabledCasAuthenticationEntryPoint(
            CasAuthenticationEntryPoint casAuthenticationEntryPoint) {
        this.casAuthenticationEntryPoint = casAuthenticationEntryPoint;
    }

    public void setRequestCache(RequestCache requestCache) {
        this.requestCache = requestCache;
    }

    public void setDoNotGateway(List<String> patterns) 
    {
        if (patterns == null)
            return;

        for (String s:patterns)
        {
            doNotGateway.add(new RegexRequestMatcher(s,null));
        }   
    }
}

Then you can just wire in the URLs like this

 <beans:property name="doNotGateway">
            <beans:list>
                <beans:value>\A/.*ajaxCall1.*\Z</beans:value>
                        <beans:value>\A/.*ajaxCall2.*\Z</beans:value>
</beans:list>
        </beans:property>

[spring-projects-issues]

Eduard Gurskiy said:

Tim, thanks! This solution will work. Honestly, it would be much better to have gateway feature support inside Spring Security. Are there any plans to officially fix this issue? By the way, at the moment we use ajax-based solution for such scenario, which goes asynchronously to CAS and if it returns any ticket, then we confidently redirect user to secured page to perform auto-login, otherwise - we leave user on unsecured page. To minimize login form content amount we use custom specific CAS theme, which returns raw data instead of login page. I can provide details to anyone interested.

[spring-projects-issues]

Michaël REMOND said:

Hello,

I'm also interested in having the CAS gateway mechanism implemented by default in Spring Security. I would be happy to submit a pull request to help the team. Therefore I would like to discuss the main implementation details with a Spring Security member before submitting.
Basically, my implementation is based on the patch submitted in 2008 :

• I have an InitiateCasGatewayAuthenticationException which inherits from AuthenticationException
• I have a TriggerCasGatewayAuthenticationFilter which has a method doCasGateway(request) who throws InitiateCasGatewayAuthenticationException when the request meets some criteria. This filter is placed after the ExceptionTranslationFilter so that the CasAuthenticationEntryPoint is called. The request is also marked as "gatewayed" using the DefaultGatewayResolverImpl from jasig Cas Client to avoid infinite loop.
• The CasAuthenticationEntryPoint is modified to set gateway=true in createRedirectUrl when the exception is InitiateCasGatewayAuthenticationException.
• Finally, the method unsuccessfulAuthentication is overriden in the CasAuthenticationFilter to check if the request was gatewayed or not. If not, we call the super implementation, otherwise we send to the initial url. It is important to note that unsuccessfulAuthentication method must be overriden because we don't want the rememberMe cookie be destroyed when we are gatewayed.

Any suggestions are welcome

[spring-projects-issues]

Rob Winch said:

This sounds fairly reasonable. One question I have is what is the proposed mechanism for determining when a gateway request should be made? For example:

• An anonymous user requests a page that does not require authentication, but desires it if possible (i.e. to display the users username)
• The application attempts to authenticate with a gateway request but fails because the user is not authenticated
• The same anonymous user requests another page that does not require authentication, but desires it if possible (i.e. to display the users username)
  ....

You can see that each request could trigger an authentication attempt. However, this is obviously not desirable. So my question is, what is the suggested mechanism to get this right? A few approaches could be:

• The CAS server specifies a cookie that is shared among the applications that just indicates if they are logged in. This doesn't break security since standard SSO still needs to occur if a user adds this cookie themselves
• A Cross Domain JS request is made to the CAS Server which (if authenticated) triggers the SSO process.

The question with these solutions is why do we need the gateway request now? To me the gateway request is no longer necessary since we already know that we should be able to successfully authenticate. It would be quite rare to have a race condition and even if so the only downside is that the user is unnecessarily prompted to authenticate. So my question is how do we support the scenario where a user optionally logs in / does not always attempt to do a gateway authentication and still need gateway support?

[spring-projects-issues]

Jérôme Leleu said:

Hi Rob,

Michaël is working in my team.

By default, the CAS authentication is only started (entry point) when you are not authenticated and try to access a protected area. This would make sense if you only login in one web application. But, as CAS is a SSO, you are certainly already authenticated in another web applications before going to a new one.
So this lead to this strange behaviour : after being authenticated and recognized in one web application, you are then anonymous in every none protected area of a new application.

Thus, the use case to have gateway configuration for some urls and no gateway configuration globally is to try to retrieve a previous CAS authentication.
On public urls, if you want to retrieve a previous CAS authentication , you need to try to authenticate using gateway=true.
On protected urls, as the user is required to be authenticated, it's not an attempted, the authentication must be successful to access (gateway=false).

About the way to detect that a CAS authentication has previously happened, you're right, we could use a cookie shared accross the domain.
But this cookie does not reflect the CAS SSO session : this is a flag to say "an authentication has occured" which lasts the web session, where as the SSO session has its own timeout policy (idle time, max time to live).
For example, you can login into a CAS server with a hard timeout of 30 minutes, access the first application and browse it 45 minutes. Then, if you try to access a new application, the domain-shared cookie still exists but your SSO session has ended, gateway=true is therefore necessary.

Thanks,
Jérôme

[spring-projects-issues]

Rob Winch said:

Jérôme,

Thus, the use case to have gateway configuration for some urls and no gateway configuration globally is to try to retrieve a previous CAS authentication.
On public urls, if you want to retrieve a previous CAS authentication , you need to try to authenticate using gateway=true.
On protected urls, as the user is required to be authenticated, it's not an attempted, the authentication must be successful to access (gateway=false).

Yes this makes sense and was as I understood it. However, as I outlined in my example, it seems that the public pages would need to hit the CAS server for every request. This does not seem very scalable to me.

For example, you can login into a CAS server with a hard timeout of 30 minutes, access the first application and browse it 45 minutes. Then, if you try to access a new application, the domain-shared cookie still exists but your SSO session has ended, gateway=true is therefore necessary.

My thought was that only the CAS server would modify the cookie and it would set shared domain cookie to timeout at the same time as the CAS session. If the session gets touched, then you would simply update the the shared domain cookie. Yes CAS services could tamper with this cookie, but the worst case scenario is that it triggers a CAS service to request the user authenticate unnecessarily.

I'm not trying to resist this feature (in fact at one point I was a voter on this issue). I really just want to understand before we add additional complexity.

[spring-projects-issues]

Jérôme Leleu said:

You're right on both points.

We can't round-trip by the CAS server every time we access a public page. That doesn't scale at all ! That said, an easy solution would be to save into the web session that we already tried a CAS authentication with gateway=true to avoid any new attempt. But we can also reuse the Jasig CAS client mechanism to remember all urls tried with gateway=true (as Michaël proposed).

We could try to make the domain cookie follow exactly the lifetime of the SSO session but it's a customization on the CAS server side, so I tend to think that it's better if we limit the custom changes and the minimal one is to add this domain cookie when the login happens. It's sufficient to make things work.

We have a pretty big CAS server installation with more than 200 web applications, most of them using Spring Security and this custom mechanism. Thus, I'm pretty confident that it will work properly in terms of performance and use cases.
We have decided to spend time to try to contribute back the main and reusable customaizations we have made in Spring Security.
The main concern for us is to turn our custom implementations into more viable ones, with satisfactory design. That's what we try to propose here (with Michaël).

[spring-projects-issues]

Rob Winch said:

My main concern is trying to find a reason to add the additional (although minimal) complexity in order to support gateway. It seems that in order to support gateway we would need to add additional logic that could be used just as easily and reliably done without gateway support. Please correct me if I am wrong.

That said, an easy solution would be to save into the web session that we already tried a CAS authentication with gateway=true to avoid any new attempt

The concern I have with remembering that we have already tried to authenticate is it seems more likely to get out of sync. For example:

• A user may come to the public landing page of a site

• An attempt to authenticate with gateway happens, but the user is not authenticated. This means we cache that attempt and will not attempt authentication in the future.

• The user leaves that CAS Service and authenticates

• The user returns to the public page and is no longer authenticated, but it is cached that an authentication attempt was already made. This prevents the user from being authenticated.

  But we can also reuse the Jasig CAS client mechanism to remember all urls tried with gateway=true

I'm not sure I followed this part. I didn't catch anything about the Jasig client being able to remember the URLs that were tried with gateway=true. In fact, I didn't know it supported this out of the box. Can one of you expand upon this?

The main concern for us is to turn our custom implementations into more viable ones, with satisfactory design. That's what we try to propose here (with Michaël).

This is much appreciated. Not only are you bringing real world use cases back to the community, but you are offering to do the coding. Again this and your patience is very much appreciated.