Spring Security's authentication.getName returns null in controller

Question

This is my first project in Spring. I am trying to get the username of the logged in user but it returns null. I have also tried the AuthenticationPrincipal annotation and other ways as well, still it returns null.

WebSecurityConfiguration class:

@EnableWebSecurity
public class WebSecurityConfiguration extends WebSecurityConfigurerAdapter{

    @Autowired
    private UserDetailsService customUserDetailsService;

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

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

    @Override
    protected void configure (HttpSecurity http) throws Exception {

        http
            .csrf().disable()
            .antMatcher("/**")
            .authorizeRequests()
                .antMatchers("/login**").permitAll()
                .anyRequest().authenticated();
    }

    public PasswordEncoder encoder() {
        return NoOpPasswordEncoder.getInstance();
    }
}

AuthorizationServerConfiguration class:

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfiguration extends AuthorizationServerConfigurerAdapter {

    @Autowired
    private AuthenticationManager authenticationManager;

    @Autowired
    private DataSource dataSource;

    @Autowired 
    private CustomUserDetailsService userDetailsService;

    @Override
    public void configure(AuthorizationServerSecurityConfigurer security) throws Exception {
        security.checkTokenAccess("isAuthenticated()");
    }

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) throws Exception {

        clients.jdbc(dataSource);
    }

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

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {

        endpoints.authenticationManager(authenticationManager)
            .tokenStore(tokenStore())
            .userDetailsService(userDetailsService)
            .approvalStoreDisabled();
    }

    @Bean 
    public TokenStore tokenStore() {
        return new JdbcTokenStore(dataSource);
    }

}

ResourceServerConfiguration class:

@Configuration
@EnableResourceServer
public class ResourceServerConfiguration extends ResourceServerConfigurerAdapter{

    @Autowired
    TokenStore tokenStore;

    @Autowired
    DataSource dataSource;

    @Override
    public void configure(ResourceServerSecurityConfigurer resources) throws Exception {
        resources.resourceId("scout").tokenStore(tokenStore);
    }

    @Override
    public void configure(HttpSecurity http) throws Exception {

        http
            .authorizeRequests()
                .antMatchers("/oauth/token", "/oauth/authorize **").permitAll();
        http
            .requestMatchers()
                .antMatchers("/api/patients/**")
                .and()
            .authorizeRequests()
                .antMatchers(HttpMethod.GET, "/api/patients/{\\d+}").access("hasAnyRole('PATIENT', 'DOCTOR')")
                .antMatchers("/api/patients/{\\d+}/medical-records").access("hasAnyRole ('PATIENT', 'DOCTOR')")
                .antMatchers("/api/patients/medical-records/{\\\\d+}/prescriptions").access("hasAnyRole('PATIENT', 'DOCTOR')")
                .antMatchers("/api/patients/**").access("hasRole('PATIENT')") 
                .and()
            .requestMatchers()
                .antMatchers("/api/doctors/**")
                .and()
            .authorizeRequests()
                .antMatchers("/api/doctors/**").access("hasRole('DOCTOR')"); 
    }
}

Below is the controller:

@GetMapping("/doctors")
public Doctor getDoctor(Authentication user) {
    System.out.println(user.getName());
    return doctorService.getDoctor(user.getName());
}

************************************Update********************************

I am using oauth2 for security. I am trying to get the username of the logged in user in my controller above. I have tried to print the Principal object and I get org.springframework.security.oauth2.provider.OAuth2Authentication@24d14be1: Principal: com.prescribr.rest.service.CustomUserDetails@56d40b2f; Credentials: [PROTECTED]; Authenticated: true; Details: remoteAddress=0:0:0:0:0:0:0:1, sessionId=<SESSION>, tokenType=bearertokenValue=<TOKEN>; Granted Authorities: ROLE_DOCTOR

On the other note, principal.getName() returns null.

I am using the access token in my header while sending the request as below in postman.

authorization: bearer theToken

CustomUserDetails class:

public class CustomUserDetails extends Users implements UserDetails {

    private static final long serialVersionUID = -8170449272852748515L;

    public CustomUserDetails(final Users user) {
        super(user);
    }

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {

        return getRoles()
                .stream()
                .map(role -> new SimpleGrantedAuthority("ROLE_" + role.getRole()))
                .collect(Collectors.toList());
    }

    @Override
    public String getPassword() {
        // TODO Auto-generated method stub
        return super.getPassword();
    }

    @Override
    public String getUsername() {
        // TODO Auto-generated method stub
        return super.getEmail();
    }

    @Override
    public boolean isAccountNonExpired() {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public boolean isAccountNonLocked() {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public boolean isCredentialsNonExpired() {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public boolean isEnabled() {
        // TODO Auto-generated method stub
        return true;
    }

}

CustomUserDetailsService class:

@Service
public class CustomUserDetailsService implements UserDetailsService {

    @Autowired
    private UsersRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String email) throws UsernameNotFoundException {

        Optional<Users> usersOptional = userRepository.findByEmail(email);

        Users user = null;

        if(usersOptional.isPresent()) {
            System.out.println(usersOptional.isPresent());
            user = usersOptional.get();
        }else {
            throw new RuntimeException("Email is not registered!");
        }

        return new CustomUserDetails(user);
    }

}

Users class:

@Entity
@Table(name="users")
public class Users {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id; 

    @Column(name="first_name")
    private String firstName;

    @Column(name="last_name")
    private String lastName;

    @Column(name="email")
    private String email;

    @Column(name="password")
    private String password;

    @Column(name="active")
    private int active;

    @OneToMany(cascade=CascadeType.ALL, 
               fetch=FetchType.EAGER
               )
    @JoinColumn(name="user_id")
    private Set<Role> roles;

    public Users() {}

    public Users(Users user) {
        this.id = user.id;
        this.firstName = user.firstName;
        this.lastName = user.lastName;
        this.email = user.email;
        this.password = user.password;
        this.active = user.active;
        this.roles = user.roles;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public int getActive() {
        return active;
    }

    public void setActive(int active) {
        this.active = active;
    }

    public Set<Role> getRoles() {
        return roles;
    }

    public void setRoles(Set<Role> roles) {
        this.roles = roles;
    }

}

Thanks again!