I tried to get a Nuxeo Platform Core Session with this way: CoreSession session = WebEngine.getActiveContext().getCoreSession();

But it isn't working.

LogServer: java.lang.IllegalStateException: Runtime not initialized

at org.nuxeo.runtime.api.Framework.checkRuntimeInitialized(Framework.java:575) ~[nuxeo-runtime-8.10.jar:na]
at org.nuxeo.runtime.api.Framework.loginAs(Framework.java:313) ~[nuxeo-runtime-8.10.jar:na]
at org.nuxeo.ecm.core.api.UnrestrictedSessionRunner.runUnrestricted(UnrestrictedSessionRunner.java:123)