Let's Encrypt is a certificate authority that provides certificates for free. (for more info : https://letsencrypt.org/)
With this plugin you are able to create a jks

If the DMZ will do public key authentication, in the user manager, set the public key path for this 'template' user to be just the three letters in uppercase: DMZ.  This will allow automatic public key verification based on keys configured on the internal server to be validated on the DMZ as well.

[attachments|dmz_publickey.png]

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!No prefs are stored on the DMZ server.