Can not cast Principal to KeycloakPrincipal in a WebFilter but no problem with servlet

Question

Environment:

• Jboss7.2
• Keycloak 6.0.1
• Java 11

I am trying to cast Principal to get Keycloak user information, but I receive a ClassCastException. WebFilter and WebServlet are in different maven modules.

org.keycloak.KeycloakPrincipal is in unnamed module of loader '[email protected]' @4d7642f0; org.keycloak.KeycloakPrincipal is in unnamed module of loader 'deployment.app.ear' @4d7682a1

Error log

cast: java.lang.ClassCastException: 
    class org.keycloak.KeycloakPrincipal cannot be cast to class org.keycloak.KeycloakPrincipal       
    (org.keycloak.KeycloakPrincipal is in unnamed module of loader '[email protected]' @4d7642f0; org.keycloak.KeycloakPrincipal is in unnamed module of loader 'deployment.app.ear' @4d7682a1
...

pom.xml (root)

...
<modules>
   <module>app-back</module> <!--where webservlet is-->
   <module>app-ejb</module> <!--where webfilter is-->
   <module>app-ear</module>
</modules>
...

WebFilter CAST KO

@WebFilter(filterName = "Filter", urlPatterns = "/*")
public class FilterPrincipal implements Filter {
    ...

    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws java.io.IOException, ServletException {
        ...
        HttpServletRequest sReq = ((HttpServletRequest) req);
        
        KeycloakPrincipal<KeycloakSecurityContext> kp = (KeycloakPrincipal<KeycloakSecurityContext>) principal;//error
        
        KeycloakSecurityContext keycloakSecurityContext = kp.getKeycloakSecurityContext();

        AccessToken token = keycloakSecurityContext.getToken();
        writer.println("username = " + token.getPreferredUsername());
        
        ...
        chain.doFilter(req, resp);
    }
    ...
    
**WebServlet CAST OK**

@WebServlet(urlPatterns = "/principal")
public class PrincipalInfoServlet extends HttpServlet {

    ...

    @SuppressWarnings("unchecked")
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {

        ...
        Principal principal = request.getUserPrincipal();
        if (principal != null) {
            ...

            // API keycloak
            if (principal instanceof KeycloakPrincipal<?>) {
                writer.println("--------------------------------");
                writer.println("Informació del token de keycloak:");

                KeycloakPrincipal<KeycloakSecurityContext> kp = (KeycloakPrincipal<KeycloakSecurityContext>) principal;//OK
                KeycloakSecurityContext keycloakSecurityContext = kp.getKeycloakSecurityContext();
    ...

Answer 1

I found a workaround by moving webservlet to maven modul app-back so the KeycloakPrincipals are in the same module.