This is just a sample servlet-based Calculator example.
Download it
and extract it to ~/apache-tomcat-9.0.38/
.
mvn clean install && cp target/mycalcwebapp.war ~/apache-tomcat-9.0.38/webapps/
Open up http://localhost:8080/mycalcwebapp/
All the security code (login, CSRF token, etc) is largely inspired or copy-pasted from https://github.com/NeilMadden/apisecurityinaction/tree/chapter04-end.