Support SSL connections

[evren]

Service Controller should provide additional options to provide the trust store parameter.

[PaulJackson123]

I was able to get SSL working, but it required adding the self-signed certificate to the JVM's cacerts.

@evren How do we set the trust store parameter? The javax.net.ssl.trustStore Java system property? Wouldn't that lead to potential conflicts? Or - we figure, let each module keep changing it, but since each nar is loaded in its own class loader, the client will get reinitialized each time? If the assignment of class loaders is at the nar level rather than the processor level then our own processors could conflict with each other.

[PaulJackson123]

ssl_notes.txt

[PaulJackson123]

Nifi has two services - StandardSSLContextService and StandardRestrictedSSLContextService - where one can set properties to identify a trust store for trusted certificates. We could take these properties and see if we can pass them to the http client. Not sure if the Java system property approach will work consistently or if we'll need to pass this to the http client through code. Need to test.