Change to allow signing of tokens on behalf of user (for use with Admin SDK calls).

Signed-off-by: Ryan Benoit <rdbenoit@me.com>
Only apply sub and prn options if they have been set.

Signed-off-by: Ryan Benoit <rdbenoit@me.com>
Merge pull request #4 from Pumpwell/master

Change to allow signing of tokens on behalf of user (for use with Admin ...