spring-security: authorization without authentication - authentication

Question

I'm trying to integrate Spring Security in my web application. It seems pretty easy to do as long as you integrate the whole process of authentication and authorization.
However, both authentication and authorization seem so coupled that it's being very time-consuming for me to understand how I could split these processes, and get authentication independently of authorization.
The authentication process is external to our system (based on single sign-on) and this cannot be modified. Nevertheless, once the user succeeds this process, it's loaded in the session, including roles.
What we are trying to achieve is to make use of this information for the authorization process of Spring Security, that's to say, to force it to get the roles from the user session instead of picking it up through the authentication-provider.
Is there any way to achieve this?

Answer 1

If your authentication is already done using an SSO service, then you should use one of spring security's pre-authentication filters. Then you can specify a UserDetails service (possibly custom) that will use the pre-authenticated user principle to populate the GrantedAuthority's
SpringSecurity includes several pre-authentication filters including J2eePreAuthenticatedProcessingFilter and RequestHeaderPreAuthenticatedProcessingFilter. If you can't find one that works for you, its also possible, and not that hard to write your own, provided you know where in the request your SSO implementation stuffs the data. (That depends on the implementation of course.)
Just implement the Filter interface and do something like this in the doFilter method:
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// principal is set in here as a header or parameter. you need to find out
// what it's named to extract it
HttpServletRequest req = (HttpServletRequest) request;
if (SecurityContextHolder.getContext().getAuthentication() == null) {
// in here, get your principal, and populate the auth object with
// the right authorities
Authentication auth = doAuthentication(req);
SecurityContextHolder.getContext().setAuthentication(auth);
}
chain.doFilter(request, response);
}

Answer 2

Yes, it's possible. Spring Security (like most of the rest of Spring) is interface-driven so that you can plug in your own implementations selectively for different parts of the framework.
Update: Spring's authorisation and authentication mechanisms work together - the authentication mechanism will authenticate the user and insert various GrantedAuthority instances in the security context. These will then be checked by the authorisation machinery to allow/disallow certain operations.
Use nont's answer for the details on how to use pre-existing authentication. The details of how you get the details from your session (e.g. roles ) will of course depend on your specific setup. But if you put in the GrantedAuthority instances derived from the roles pre-populated in your session by your SSO system, you will be able to use them in your authorisation logic.
From the reference documentation (slightly edited, with my emphasis):
You can (and many users do) write
their own filters or MVC controllers
to provide interoperability with
authentication systems that are not
based on Spring Security. For example,
you might be using Container Managed
Authentication which makes the current
user available from a ThreadLocal or
JNDI location. Or you might work for a
company that has a legacy proprietary
authentication system, which is a
corporate "standard" over which you
have little control. In such
situations it's quite easy to get
Spring Security to work, and still
provide authorization capabilities.
All you need to do is write a filter
(or equivalent) that reads the
third-party user information from a
location, build an Spring
Security-specific Authentication
object, and put it onto the
SecurityContextHolder. It's quite easy
to do this, and it is a
fully-supported integration approach.

Answer 3

The server that handles the authentication should redirect the user to the application passing to it some kind of key (a token in CAS SSO). Then the application use the key to ask to the authentication server the username and roles associated. With this info create a security context that is passed to the authorization manager. This is a very simplified version of a SSO login workflow.
Take a look to CAS SSO and CAS 2 Architecture.
Tell me if you need more information.

Answer 4

we have had the same requirement where we had to use spring security for authorization purpose only. We were using Siteminder for authentication. You can find more details on how to use authorization part of spring security not authentication here at http://codersatwork.wordpress.com/2010/02/13/use-spring-security-for-authorization-only-not-for-authentication/
I have also added source code and test cases at http://code.google.com/p/spring-security-with-authorization-only/source/browse/

Answer 5

I am trying to understand CAS authentication with our own Authorization and was getting confused since the User object in Spring Security always expects the password to be filled in and we don't care about that in our scenario. After reading Surabh's post, it seems that the trick is to return a custom User object without the password filled in. I will try that out and see if it works in my case. Hopefully no other code in the chain will be expecting the Password in the User object.

Answer 6

I use the authorization by this:
Inject the authorization related bean into my own bean:
#Autowired
private AccessDecisionManager accessDecisionManager;
#Autowired
FilterSecurityInterceptor filterSecurityInterceptor;
Use this bean by this:
FilterInvocation fi = new FilterInvocation(rundata.getRequest(), rundata.getResponse(), new FilterChain() {
public void doFilter(ServletRequest arg0, ServletResponse arg1) throws IOException, ServletException {
// TODO Auto-generated method stub
}
});
FilterInvocationDefinitionSource objectDefinitionSource = filterSecurityInterceptor.getObjectDefinitionSource();
ConfigAttributeDefinition attr = objectDefinitionSource.getAttributes(fi);
Authentication authenticated = new Authentication() {
...........
public GrantedAuthority[] getAuthorities() {
GrantedAuthority[] result = new GrantedAuthority[1];
result[0] = new GrantedAuthorityImpl("ROLE_USER");
return result;
}
};
accessDecisionManager.decide(authenticated, fi, attr);

Answer 7

I too did spent lot of hours investigating on how to implement custom authorization without authentication.
The authentication process is external to our system (based on single sign-on).
I have done it, as mentioned below and it Works!!! (I am sure there are many other ways to it better, but this way just suits my scenario well enough)
Scenario : User is already authenticated by external system and all information needed for authorization is present in the request
1.
Security config need to be created, enabling global method security as below.
#Configuration
#EnableWebSecurity
#EnableGlobalMethodSecurity(securedEnabled = true, prePostEnabled = true)
class SpringWebSecurityConfig extends WebSecurityConfigurerAdapter {
#Override
protected void configure(final HttpSecurity http) throws Exception {
}
}
2.) Implement Spring PermissionEvaluator to authorize whether the request should be allowed or rejected
#Component
public class CustomPermissionEvaluator implements PermissionEvaluator {
public boolean authorize(final String groups, final String role) {
boolean allowed = false;
System.out.println("Authorizing: " + groups + "...");
if (groups.contains(role)) {
allowed = true;
System.out.println(" authorized!");
}
return allowed;
};
#Override
public boolean hasPermission(final Authentication authentication, final Object groups, final Object role) {
return authorize((String) groups, (String) role);
};
#Override
public boolean hasPermission(final Authentication authentication, final Serializable targetId, final String targetType, final Object permission) {
return authorize((String) targetId, (String) permission);
};
}
3.) Add MethodSecurityConfig
#Configuration
#EnableGlobalMethodSecurity(prePostEnabled = true)
public class MethodSecurityConfig extends GlobalMethodSecurityConfiguration {
#Override
protected MethodSecurityExpressionHandler createExpressionHandler() {
DefaultMethodSecurityExpressionHandler expressionHandler = new DefaultMethodSecurityExpressionHandler();
expressionHandler.setPermissionEvaluator(new CustomPermissionEvaluator());
return expressionHandler;
}
}
4.) Add #PreAuthorize in your controller as shown below. In this example, all the groups of the user are present in request header with key 'availableUserGroups'.
This is then passed on to the CustomPermissionEvaluator to verify authorization. Please note that spring automatically passes Authentication object to the method 'hasPermission'.
So in case if you want to load user and check using spring 'hasRole' method, then this can be used.
#PreAuthorize("hasPermission(#userGroups, 'ADMIN')")
#RequestMapping(value = "/getSomething")
public String getSomething(#RequestHeader(name = "availableUserGroups") final String userGroups) {
return "resource allowed to access";
}
Handling Other Scenarios :
1.) In scenario where you want to load the user before you can perform the authorization. You can use spring pre-authentication filters, and do it in a similar way.
Example link : http://www.learningthegoodstuff.com/2014/12/spring-security-pre-authentication-and.html