CAS Authorization: A Practical Guide

TL;DR

Yes, Central Authentication Service (CAS) can handle authorization, but it’s not its primary function. CAS excels at authentication – verifying who a user is. For authorization – deciding what a user can do – you typically need to integrate CAS with other systems or use CAS attributes and release policies.

Understanding the Difference

Before diving into how, let’s clarify:

• Authentication: Proving identity (e.g., username/password check).
• Authorization: Granting access to resources based on that identity (e.g., role-based access control).

CAS focuses on the first part. Authorization often requires more complex logic than CAS provides out of the box.

Methods for Implementing Authorization with CAS

1. Using Attributes and Release Policies
   • CAS can release user attributes (e.g., roles, group memberships) to applications after successful authentication.
   • Applications then use these attributes to make authorization decisions.
   • Configure CAS to release the necessary attributes in cas.properties:

   attributeRepository = myAttributeRepository
   releasePolicy = allowAll
   

   Important: The allowAll policy is generally not recommended for production environments as it releases all attributes. Define a more restrictive release policy based on your application’s needs.

   • Example attribute repository (Java):

   public class MyAttributeRepository implements AttributeRepository {
     @Override
     public Set<String> getAttributesFor(String principal, Credential credential) {
       Set<String> attributes = new HashSet<>();
       // Logic to fetch user roles from a database or other source
       if (principal.equals("user1")) {
         attributes.add("ROLE_ADMIN");
       } else {
         attributes.add("ROLE_USER");
       }
       return attributes;
     }
   }
   

2. Integrating with an Authorization Server (e.g., OAuth 2.0, OpenID Connect)
   • CAS can act as an identity provider (IdP) for an authorization server.
   • The authorization server handles the complex authorization logic and issues access tokens to applications.
   • This is a more robust solution for complex scenarios.
   • You’ll need to configure CAS to support the relevant protocols (e.g., OpenID Connect).
3. Using Proxy Tickets and Application-Level Authorization
   • CAS can issue proxy tickets, allowing applications to request authorization information from other services on behalf of the user.
   • Applications are responsible for interpreting these tickets and making authorization decisions.
   • This approach requires more development effort but provides greater flexibility.
4. Custom CAS Filters
   • You can write custom filters to intercept requests and perform authorization checks based on user attributes or other criteria.
   • This is the most flexible option, but it requires a deep understanding of the CAS architecture.

Example Scenario: Role-Based Access Control

1. Configure CAS to release user roles as attributes (as shown in step 1).
2. In your application, retrieve the user’s roles from the CAS ticket.
3. Implement role-based access control logic based on these roles. For example:

// Example Java code
String[] roles = (String[]) session.getAttribute("roles");
if (Arrays.asList(roles).contains("ROLE_ADMIN")) {
  // Allow access to admin features
} else {
  // Deny access or redirect to an error page
}

Security Considerations

• Attribute Release Policy: Carefully control which attributes are released to applications. Avoid releasing sensitive information unnecessarily.
• Trust Relationships: Ensure that you trust the applications receiving CAS tickets.
• Input Validation: Validate all user input and attribute values to prevent security vulnerabilities.