The end goal is to have a Spring Boot app that works with an XA transaction coordinator, in particular that coordinator would be Narayana.
We think that since Wildfly uses IronJacamar, Spring Boot could use it too.
Where can we find examples of this, or some instruction to get us there quickly?
The IronJacamar is used as the JCA and pooling library for WildFly but for other projects the Narayana can be configured to used other libraries. IronJacamar is fully fledged implementation of the Java EE JCA specifiation which is often not necessary when running on runtimes like Quarkus or Spring.
For example within Quarkus (https://quarkus.io/) there is used Agroal (https://github.com/agroal/agroal), for Apache Tomcat it could be DBCP2 (https://github.com/web-servers/narayana-tomcat).
For Narayana and Spring integration it could be recommended to work with the Snowdrop extension - https://github.com/snowdrop/narayana-spring-boot - where DBCP2 (instead of IronJacamar) is used.