On starting a new Weblogic Portal 10.3.6 domain created from a template of a previously created domain, you see this error:
Caused by: javax.servlet.ServletException: [Security:090820]The internal variable ServletInfoSpi is null and it should not be at weblogic.security.providers.saml.SAMLServletAuthenticationFilter.init(SAMLServletAuthenticationFilter.java:51
As noted in this post here, the *.jks keystore files are omitted when creating from a template (is this a defect?). Copy them across from a new domain created via the config wizard into the root dir of your newly created domain fixes the issue:
[mwhome]\user_projects\domains\your_domain\*.jks