FCM client
Forked from google/fcm, but kept only the HTTP client part.
I did this, because I needed support for content_available
and FCM, which were both added in master branch, which has not been released yet.
<dependency>
<groupId>com.bertoncelj</groupId>
<artifactId>fcm-client</artifactId>
<version>1.1.0</version>
</dependency>
See original project's readme for other info.