A DESCRIPTION OF THE PROBLEM :
In its current state, the Poly1305 algorithm in Java cannot be used on its own like in BouncyCastle for instance (https://github.com/bcgit/bc-java/blob/master/core/src/main/java/org/bouncycastle/crypto/macs/Poly1305.java).

It would be useful to be able to use it on its own as a MAC.