Another proposed standard is REST-AT which had undergone some development by RedHat but still didn't get out of the draft stage. It's however supported by the WildFly application server out-of-the-box.

This standard allows using the application server as a transaction coordinator with a specific REST API for creating and joining the distributed transactions.

The RESTful web services that wish to participate in the two-phase transaction also have to support a specific REST API.

Unfortunately, to bridge a distributed transaction to local resources of the microservice, we'd still have to either deploy these resources to a single JTA platform or solve a non-trivial task of writing this bridge ourselves.