Every new Play app gets a new application secret generated into its config file.
application.secret=asdfadsfdasf
I\'m developing an open source app
It looks like that secret is important, but you can generate new ones for production vs development. So for development you could check it into SVN then generate a different one for production.
http://www.playframework.org/documentation/1.0/production
You can externalize the secret as an environment variable.
In conf/application.conf
Simply replace
application.secret=abc123...
with
application.secret=${APP_SECRET}
and then set this config var in Heroku with:
$ heroku config:add APP_SECRET=abc123...
Now you can manage secrets on a per-app basis and avoid checking them into version control.