SAML? JAVA check ( non spring )

Hello poster.
Our service use java 1.8, AWS tomcat.
I applied for okta certification provide sso url, entity id and I was offered idp sso url, idp issuser, idp metadata, idp certificate.
but unfortunately Our service not used spring unlike other systems.
There are a lot of samples, so can you tell us which part I should look at?
We need that user is logged in? and what is user id
I’ll be waiting for the reply
Thank you