Pros of Spring Security

• More comprehensive security framework, covering a wider range of application security needs
• Seamless integration with Spring ecosystem and other Spring projects
• Larger community and more frequent updates

Cons of Spring Security

• Steeper learning curve due to its extensive feature set
• Can be overkill for simpler authentication requirements
• Configuration can be complex for advanced scenarios

Code Comparison

Spring Security configuration example:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
            .antMatchers("/public/**").permitAll()
            .anyRequest().authenticated()
            .and().formLogin();
    }
}

CAS configuration example:

cas.server.name=https://cas.example.org:8443
cas.server.prefix=${cas.server.name}/cas
logging.config=file:/etc/cas/config/log4j2.xml

Spring Security offers more granular control over security configurations within the application code, while CAS typically relies on external configuration files for its setup. Spring Security's approach allows for more flexibility in defining security rules, but CAS provides a simpler configuration for standard use cases.

Pros of Keycloak

• More comprehensive identity and access management solution, offering features beyond authentication
• Easier setup and configuration with a user-friendly admin console
• Better support for modern protocols like OAuth 2.0 and OpenID Connect out of the box

Cons of Keycloak

• Higher resource consumption, potentially less suitable for lightweight deployments
• Steeper learning curve for advanced customizations and extensions
• Less flexibility in certain authentication scenarios compared to CAS

Code Comparison

Keycloak (Java)

public class CustomAuthenticator implements Authenticator {
    @Override
    public void authenticate(AuthenticationFlowContext context) {
        // Custom authentication logic
    }
}

CAS (Java)

public class CustomAuthenticationHandler implements AuthenticationHandler {
    @Override
    public AuthenticationHandlerExecutionResult authenticate(Credential credential) {
        // Custom authentication logic
    }
}

Both projects use Java and follow similar patterns for extending authentication functionality. Keycloak's approach is more focused on authentication flows, while CAS provides a more direct handler-based approach. The code structures reflect their respective architectures and design philosophies.

Pros of pac4j

• Lightweight and flexible authentication/authorization library
• Supports multiple protocols and frameworks
• Easy integration with various Java web technologies

Cons of pac4j

• Less comprehensive out-of-the-box features compared to CAS
• Requires more configuration and setup for complex scenarios
• Smaller community and ecosystem

Code Comparison

pac4j example:

Config config = new Config(new GoogleClient("clientId", "secret"));
SecurityFilter filter = new SecurityFilter(config, "GoogleClient");

CAS example:

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    http.authorizeRequests()
        .antMatchers("/secure").authenticated()
        .and().csrf().disable();
    return http.build();
}

pac4j focuses on providing a flexible authentication engine, while CAS offers a more comprehensive single sign-on solution. pac4j's code tends to be more concise and adaptable to different scenarios, whereas CAS provides a more structured approach with built-in security features.

Both projects have their strengths, with pac4j being more suitable for developers who need fine-grained control over authentication mechanisms, and CAS being better for organizations looking for a complete SSO solution with extensive features out of the box.