@GET
@Path("get/{id}")
@Produces(MediaType.APPLICATION_JSON)
public UserEntityDo getUserDetail(@HeaderParam("token") String token, @PathParam("id") String id) {
  // Check token validity and return corresponding user name if any
  String username = checkToken(token); 
  if (username == null) {
    Response.status(Response.Status.FORBIDDEN).build();
  }
  Subject subject = new Subject();
  subject.getPrincipals().add(new SimplePrincipal(username));
  subject.setReadOnly();
  RunContext runContext = RunContexts.empty().withSubject(subject);
  Map<String, Object> data = runContext.call(new Callable<Map<String, Object>>() {
    @Override
    public Map<String, Object> call() throws Exception {
      return BEANS.get(IUserService.class).getData(UUID.fromString(id));
    }
  });
  // Build user entity data
  UserEntityDo user = BEANS.get(UserEntityDo.class).withLogin((String) data.get("login"))
      .withLastLoginDate((Date) data.get("lastLoginDate").withFirstName((String) data.get("firstName").withLastName((String) data.get("lastName"));
  return user;
}

import java.io.IOException;

import javax.security.auth.Subject;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.scout.rt.platform.context.RunContexts;
import org.eclipse.scout.rt.platform.security.SimplePrincipal;

public class TokenFilter implements Filter {

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse resp = (HttpServletResponse) response;

    String token = getToken(req);
    String username = checkToken(token);
    if (username == null) {
      resp.sendError(HttpServletResponse.SC_FORBIDDEN);
    } else {
      Subject subject = createSubject(username);
      RunContexts.copyCurrent(true)
          .withSubject(subject)
          .run(() -> chain.doFilter(request, response));
    }
  }

  protected String getToken(HttpServletRequest req) {
    // Extract token from HTTP request
    return req.getHeader("token");
  }

  protected String checkToken(String token) {
    // Convert token to username
    return ...;
  }
  
  protected Subject createSubject(String username) {
    // Create subject from username
    Subject subject = new Subject();
    subject.getPrincipals().add(new SimplePrincipal(username));
    subject.setReadOnly();
    return subject;
  }

  @Override
  public void destroy() {
  }
}