Make jsrsigner Idiomatic

edit

I believe that what you are looking for is the exec's creates, onlyif, and unless attributes. As noted here, the command attribute of an exec must be idempotent. There are three ways to do so - the command itself is idempotent, refreshonly is set to true, or through the use of the three listed attributes. It seems likely that you want the creates attribute, like so:

   exec { 'sign jars':
     cwd     => "/home/user/app/jars",
     creates => '/home/user/app/jars/signing.txt',
     command => "sudo su - user -c 'cd /home/user/app/jars;find . -iname \"*.jar\" | xargs -i jarsigner -verbose -certs -keystore JAWS.key -storepass user{} app>signing.txt'",
     timeout => 900,
   }

It may be more appropriate to use unless/onlyif and verify the contents of signing.txt. Check the documentation of the attributes to determine which satisfies your needs the best.