Return custom Spring security message from Rest API

I want to create custom error message for Forbidden error. I tried this:

Spring Security Configuration:

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true)
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

  @Autowired
  private JwtTokenProvider jwtTokenProvider;

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

    // Disable CSRF (cross site request forgery)
    http.csrf().disable();

    // No session will be created or used by spring security
    http.sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS);

    // Entry points
    http.authorizeRequests()//
        .antMatchers("/users/signin").permitAll()//
        .antMatchers("/users/signup").permitAll()//
        .antMatchers("/h2-console/**/**").permitAll()
        // Disallow everything else..
        .anyRequest().authenticated();

    // If a user try to access a resource without having enough permissions
    http.exceptionHandling().accessDeniedHandler(accessDeniedHandler());

    // Apply JWT
    http.apply(new JwtTokenFilterConfigurer(jwtTokenProvider));

    // Optional, if you want to test the API from a browser
    // http.httpBasic();
  }

  @Override
  public void configure(WebSecurity web) throws Exception {
    // Allow swagger to be accessed without authentication
    web.ignoring().antMatchers("/v2/api-docs")//
        .antMatchers("/swagger-resources/**")//
        .antMatchers("/swagger-ui.html")//
        .antMatchers("/configuration/**")//
        .antMatchers("/webjars/**")//
        .antMatchers("/public")

        // Un-secure H2 Database (for testing purposes, H2 console shouldn't be unprotected in production)
        .and()
        .ignoring()
        .antMatchers("/h2-console/**/**");
  }

  @Bean
  public PasswordEncoder passwordEncoder() {
    return new BCryptPasswordEncoder(12);
  }

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

  @Bean
  public AccessDeniedHandler accessDeniedHandler() {
    return new CustomAccessDeniedHandler();
  }

}

Custom handler:

public class CustomAccessDeniedHandler implements AccessDeniedHandler {

    public static final Logger LOG = LoggerFactory.getLogger(CustomAccessDeniedHandler.class);

    @Override
    public void handle(HttpServletRequest request, HttpServletResponse response, AccessDeniedException exc) throws IOException, ServletException {
        response.setStatus(HttpStatus.UNAUTHORIZED.value());

        String jsonPayload = "{\"messffffffage\" : \"%s\", \"timestamp\" : \"%s\" }";
        response.getOutputStream().println(String.format(jsonPayload, exc.getMessage(), Calendar.getInstance().getTime()));
    }
}

But I get the default error message:

{
    "timestamp": "2020-06-09T21:23:32.528+00:00",
    "status": 403,
    "error": "Forbidden",
    "message": "",
    "path": "/engine/users/request"
}

Do you know how I can implement the handler proprly?

Just add AuthenticationEntryPoint

@Component
public class JwtAuthenticationEntryPoint implements AuthenticationEntryPoint {

    @Override
    public void commence(HttpServletRequest request, HttpServletResponse response,
                         AuthenticationException authException) throws IOException {

        response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Unauthorized");
    }
}

and configure it in configuration class

@Autowired
    private JwtAuthenticationEntryPoint jwtAuthenticationEntryPoint;

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

        httpSecurity.csrf().disable()
                .authorizeRequests().antMatchers("/authenticate").permitAll()
                .anyRequest().authenticated()


                .and().
                exceptionHandling().authenticationEntryPoint(jwtAuthenticationEntryPoint)


                .and().sessionManagement()
                .sessionCreationPolicy(SessionCreationPolicy.STATELESS);
        httpSecurity.addFilterBefore(requestFilter, UsernamePasswordAuthenticationFilter.class);
    }

you can write custom message in JwtAuthenticationEntryPoint (name is user defined) class which implements AuthenticationEntryPoint

just add your custom message in the response.sendError(...) method.