There are number of built-in AuthenticationManager in Spring Security that can be easily used in your application. Spring Security also has a number of helper classes, using which you can set up AuthenticationManager. One helper class is AuthenticationManagerBuilder. Using this class, its quite easy to set up UserDetailsService against a database, in memory, in LDAP, and so on. If the need arises, you could also have your own custom UserDetailsService (maybe a custom single sign-on solution is already there in your organization).

You can make an AuthenticationManager global, so it will be accessible by your entire application. It will be available for method security and other WebSecurityConfigurerAdapter instances. WebSecurityConfigurerAdapter is a class that is extended by your Spring configuration file, making it quite easy to bring Spring Security into your Spring application. This is how you set up a global AuthenticationManager using the @Autowired annotation:

@Configuration
@EnableWebSecurity
public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {
     
    @Autowired
    public void confGlobalAuthManager(AuthenticationManagerBuilder auth) throws 
            Exception {
        auth
            .inMemoryAuthentication()
                .withUser("admin").password("admin@password").roles("ROLE_ADMIN");
    }
}

You can also create local AuthenticationManager, which is only available for this particular WebSecurityConfigurerAdapter, by overriding the configure method, as shown in the following code:

@Configuration
@EnableWebSecurity
public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {
     
    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth
            .inMemoryAuthentication()
                .withUser("admin").password("admin@password").roles("ROLE_ADMIN");
    }
}

Another option is to expose the AuthenticationManager bean by overriding authenticationManagerBean method, as shown here:

@Override
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
}

You can also expose various AuthenticationManager, AuthenticationProvider, or UserDetailsService as beans which will override the default ones.

In the preceding code examples we have used AuthenticationManagerBuilder to configure in-memory authentication. More mechanisms of the AuthenticationManagerBuilder class will be used in the subsequent examples in this chapter.