To complete idelpivnitskiy's work his feature branch webpush-variant (#750) should be re-based with master branch and then integrated with a working web push library. There is a good open-source web push library which its maven dependency is as followes:

<dependency>
<groupId>nl.martijndwars</groupId>
<artifactId>web-push</artifactId>
<version>3.1.1</version>
</dependency>

An integration between this library and webpush-variant branch is needed to add web push functionality to aerogear unified push server.