How to query users by user id in spring security?

I have a Spring Boot app with Spring Security where I have extended the org.springframework.security.core.userdetails.User class to create a custom user object.I am hard-coding users since I only need a few to test out some feaures.How can I query and fetch a certain user based on its user-id or email-id,which are custom variables I have added ?Is there a way to do this without shifting to jdbc authentication etc,since I feel it might complicate it too much ?

My custom user class:

import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.userdetails.User;
import java.util.Collection;
import java.util.List;

public class Guest extends User {
    public Guest(String username, String password, boolean enabled, boolean accountNonExpired,
                       boolean credentialsNonExpired, boolean accountNonLocked,
                       Collection<? extends GrantedAuthority> authorities) {
        super(username, password, enabled, accountNonExpired, credentialsNonExpired, accountNonLocked, authorities);
    }
    private long id;
    private String firstName;
    private String lastName;
    private String emailAddress;
    private String phoneNumber;
    
    //some getters and setters

    public Guest(long id, String firstName, String lastName, String emailAddress, String phoneNumber, String username, String password, List<GrantedAuthority> authorities,
                 boolean enabled, boolean accountNonExpired, boolean credentialsNonExpired, boolean accountNonLocked) {


        super(username, password, enabled, accountNonExpired, credentialsNonExpired,
                accountNonLocked, authorities) ;
        this.id=id;
        this.firstName=firstName;
        this.lastName=lastName;
        this.emailAddress=emailAddress;
        this.phoneNumber=phoneNumber;
    }
}

My new userdetailsService class:

@Service("userDetailsService")
public class MyUserDetailsService implements UserDetailsService {
    private static List<Guest> users = new ArrayList();

    public MyUserDetailsService() { 
    //hard-coding users
}
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    //building user here
}

SecurityConfig.java

@Configuration
@EnableWebSecurity
public class ApplicationSecurityConfiguration extends WebSecurityConfigurerAdapter{
    
    @Autowired
    @Qualifier("userDetailsService")
    private UserDetailsService userDetailsService;

    @Bean
    public BCryptPasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    };

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(userDetailsService).passwordEncoder(passwordEncoder());
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
       //authorization logic here        
    }

}

You can do like below sample with hardcoded values.. if you needed it for mock implementation

public UserDetails loadUserByUsername(String userName){
		
//use your custom 'List<Guest> users' hardcoded values to create User object

User user = new User(username, password, enabled, accountNonExpired, credentialsNonExpired, accountNonLocked,
				authorities);
return user;
}

note:- loadUserByUsername(String username).. here userName can be userToken containing any info you want as ref. (which usually you use to query db for fetching usrname & pass) .. in this cases lets say Id.. once you get id (as userToken/userName) above you can compare with ur guest list to load User object