I achieved setup some variables writing directly in the openfire.xml file, however I got stuck in the admin user creation. I’ve tried to create it with the Openfire REST API plugin but it doesn’t work.
Automated setup has been implemented in not yet released 4.3.0 version https://issues.igniterealtime.org/browse/OF-1412
You can test it with Beta. https://www.igniterealtime.org/downloads/beta.jsp
Currently there is a bug in this version. After installing this version on top of 4.2.3 one needs to remove Openfire\plugins\admin\webapp\WEB-INF\lib folder manually for Admin Console to work.