A custom AuthenticationEntryPoint can be used to set necessary response headers, content-type, and so on before sending the response back to the client.

The org.springframework.security.web.authentication.www.BasicAuthenticationEntryPoint class is a built-in AuthenticationEntryPoint implementation, which will get invoked for basic authentication to commence. A custom entry point can be created by implementing the org.springframework.security.web.AuthenticationEntryPoint interface. The following is an example implementation:

@Component
public final class CustomAuthenticationEntryPoint implements 
        AuthenticationEntryPoint {
    @Override
    public void commence(final HttpServletRequest request, final 
            HttpServletResponse response, final AuthenticationException 
        authException) throws IOException...