Wildfly 27 Redirected login results in AuthenticationStatus.SEND_CONTINUE & AnonymousCallerPrincipal

Question

I have the same issue as in this other ticket, but I have identified that I receive SEND_CONTINUE when a redirect or forward to the login form occurs. Also, I'm using Wildfly 27.0.1, with Jakarta bindings (jakarta. namespace).

Relevant items...
ApplicationConfig.java:

@CustomFormAuthenticationMechanismDefinition(loginToContinue =         
@LoginToContinue(loginPage = "/login.xhtml", useForwardToLogin = true))
@FacesConfig
@ApplicationScoped
public class ApplicationConfig {
}

web.xml

<security-constraint>
    <web-resource-collection>
        <web-resource-name>index</web-resource-name>
        <url-pattern>/index.xhtml</url-pattern>
    </web-resource-collection>
    <auth-constraint>
        <role-name>ADMINISTRATOR</role-name>
        <role-name>USER</role-name>
    </auth-constraint>
</security-constraint>

LoginBacking.java:

public void login() throws IOException {
    switch (continueAuthentication()) {
    case SEND_CONTINUE:
        facesContext.responseComplete();
        break;
    case SEND_FAILURE:
        facesContext.addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR, "Login failed", null));
        break;
    case SUCCESS:
        facesContext.addMessage(null, new FacesMessage(FacesMessage.SEVERITY_INFO, "Login succeeded", null));
        externalContext.redirect(externalContext.getRequestContextPath() + "/index.xhtml");
        break;
    case NOT_DONE:
        facesContext.addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR, "Login failed", null));
        break;
    }
}

private AuthenticationStatus continueAuthentication() {
    return securityContext.authenticate((HttpServletRequest) externalContext.getRequest(),
            (HttpServletResponse) externalContext.getResponse(),
            AuthenticationParameters.withParams().credential(new UsernamePasswordCredential(username, password)));
}

Authentication is handled by a JSR-375 identity store, which is being called correctly, and is returning correctly.

If I go to index.xhtml, and get the login page, authentication always returns SEND_CONTINUE. If I go to login.xhtml, authentication always returns SUCCESS. Further, while SecurityContext.getCallerPrincipal is not null, it is an instance of AnonymousCallerPricinipal, rather than the caller principal I return from my IdentityStore. Notice that this behavior does not depend on the useForwardToLogin setting.

Notice that nowhere do I have a "multipart authentication" configured.

Anyone have any up to date thoughts on this?