The JAR signer is pluggable, so that one can adapt the signing to their own needs. For example, one may want for example to use a server side JAR signing solution ( provides an example of such a signing implementation).
See src/test/projects/project5 as an example on how to use an external JAR signer.
This was deprecated, since 1.0-beta-2, perharps I did not see the point ?