To configure the SSLEngine used by Play as a server, extend this class. In particular, if you want to call
sslEngine.setNeedClientAuth(true), this is the place to do it.
If you want to specify your own SSL engine, define a class implementing this interface. If the implementing class
takes ApplicationProvider in the constructor, then the applicationProvider is passed into it, if available.
The path to this class should be configured with the system property
the SSL engine to be used for HTTPS connection.