how to get client assertion ok okta
curl -v -X POST \
-H "Content-type:application/x-www-form-urlencoded" \
"https://${yourOktaDomain}/oauth2/default/v1/token" \
-d "client_id={client_id}&client_secret={client_secret}&grant_type=authorization_code&redirect_uri={redirect_uri}&code={code}"