read16.md

Spring Authentication

Spring Security Architecture

1. Authentication and Access Control

• Authentication

public interface AuthenticationManager {

  Authentication authenticate(Authentication authentication)
    throws AuthenticationException;
}

• Authorization, AKA: Access Control

The main strategy interface for authentication is AuthenticationManager, which has only one method:

public interface AuthenticationManager {

  Authentication authenticate(Authentication authentication)
    throws AuthenticationException;
}

• An AuthenticationManager can do one of 3 things in its authenticate() method:

1. Return an Authentication (normally with authenticated=true), if input represents a valid principal.

2. Throw an AuthenticationException (which is a runtime exception.) if input represents an invalid principal.

3. Return null if it cannot decide.

• The most commonly used implementation of AuthenticationManager is ProviderManager, which delegates to a chain of AuthenticationProvider instances.
• An AuthenticationProvider is a bit like an AuthenticationManager, but it has an extra method to allow the caller to query whether it supports a given Authentication type:

public interface AuthenticationProvider {

	Authentication authenticate(Authentication authentication)
			throws AuthenticationException;

	boolean supports(Class<?> authentication);
}

2. Customizing Authentication Managers

• The most commonly used configuration helper is the AuthenticationManagerBuilder.

@Configuration
public class ApplicationSecurity extends WebSecurityConfigurerAdapter {

   ... // web stuff here

  @Autowired
  public void initialize(AuthenticationManagerBuilder builder, DataSource dataSource) {
    builder.jdbcAuthentication().dataSource(dataSource).withUser("dave")
      .password("secret").roles("USER");
  }

}

• The AuthenticationManagerBuilder is @Autowired into a method in a @Bean.

@Configuration
public class ApplicationSecurity extends WebSecurityConfigurerAdapter {

  @Autowired
  DataSource dataSource;

   ... // web stuff here

  @Override
  public void configure(AuthenticationManagerBuilder builder) {
    builder.jdbcAuthentication().dataSource(dataSource).withUser("dave")
      .password("secret").roles("USER");
  }

}

• If we had used an @Override of a method in the configurer, the AuthenticationManagerBuilder would be used only to build a “local” AuthenticationManager, which would be a child of the global one.
• In a Spring Boot application, you can @Autowired the global one into another bean, but you cannot do that with the local one unless you explicitly expose it yourself.

3. Authorization or Access Control

• The core Authorization is AccessDecisionManager.
• There are three implementations provided by the framework and all three delegate to a chain of AccessDecisionVoter instances.

4. Web Security

The typical layering of the handlers for a single HTTP request:

• The client sends a request to the application, and the container decides which filters and which servlet apply to it based on the path of the request URI.

• At most, one servlet can handle a single request, but filters form a chain, so they are ordered.

• The order of the filter chain is very important, and Spring Boot manages it through two mechanisms: @Beans of type Filter can have an @Order or implement Ordered, and they can be part of a FilterRegistrationBean that itself has an order as part of its API.

• In a Spring Boot application, the security filter is a @Bean in the ApplicationContext, and it is installed by default so that it is applied to every request.

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Spring Auth cheat sheet

• a cheat sheet for Spring Authentication