Hi Marek,
thank you for the advice. It helped me. Just small correction - the web.xml is located in /modules/system/layers/keycloak/org/keycloak/keycloak-server-subsystem/main/server-war/WEB-INF/web.xml (in my Keycloak 1.9.3.Final). The filter definition looks then like follows:
<filter>
<filter-name>Keycloak Session Management</filter-name>
<filter-class>org.keycloak.services.filters.KeycloakSessionServletFilter</filter-class>
<async-supported>true</async-supported>
</filter>
Before applying the filter settings I found a small trick how to do the same by putting two lines in the code:
ServletRequestContext context = ServletRequestContext.current();
context.setAsyncSupported(true);
Anyway, I will create a JIRA for this.
Thank you&Best regards,
Bystrik