The page, "Properties that affect behavior of RIAs", describes the usage of the javaws.cfg.jauthenticator property. The properties page is linked from the "JNLP File Syntax page" (near where the secure properties are listed).
Per Andy Herrick, this is sufficient.
See urls below:
Properties that affect behavior of RIAs page in jdk 7 repo -
JNLP file syntax page in jdk7 repo -