KiwiSecurity and SimpleSSLContextFactory should support JCE providers

[sleberknight]

While implementing #940 I realized that neither KiwiSecurity nor SimpleSSLContextFactory support a key store provider or a trust store provider that would be passed into KeyStore#getInstance(String type, String provider) when they are created. We can add support for this in both of these classes. We should also consider adding support in SSLContextConfiguration, since then these values could be passed all the way from a TlsContextConfiguration, e.g.

var tlsContextConfig = getTlsContextConfiguration();
var sslContext = tlsContextConfig.toSslContextConfiguration().toSSLContext();

We might also want to add convenience methods directory to TlsContextConfiguration to allow creating an SSLContext directly¹ and/or converting to a SimpleSSLContextFactory, e.g.

var tlsContextConfig = getTlsContextConfiguration();
var sslFactory = tlsContextConfig.toSimpleSSLContextFactory();
var sslContext = sslFactory.getSslContext();

or directly...

var tlsContextConfig = getTlsContextConfiguration();
var sslContext = tlsContextConfig.toSSLContext();

There are probably more things that can be added to provide as much flexibility as needed, but without making things overly complex, since the properties come from the XxxContextConfiguration classes which then allow you to create the SimpleSSLContextFactory and/or the SSLContext.

Currently, the SimpleSSLContextFactory has three telescoping constructors and a builder. From this point on, we should not add any more (public) constructors since (a) telescoping constructors are generally an anti-pattern and (b) we have the builder which can support any new properties we want to add. We will need to maintain a private all-args constructor that will need to be updated any time we add new properties, and this will be called by the builder and also by one of the public constructors (the one with the most arguments, which is called by the other public constructors).

Footnotes

1. Actually this functionality already exists because TlsContextConfiguration implements KeyAndTrustStoreConfigProvider which in turn extends TrustStoreConfigProvider which defines both toSSLContext() and toSslSocketFactory() methods. So we can already convert directly to those without going first to a SimpleSSLContextFactory. As a result, it might not add much value to add a method to convert to SimpleSSLContextFactory. The one reason to do so might be that once SimpleSSLContextFactory builds an SSLContext it caches it, and then always returns that same instance, which I am (pretty sure) is safe to do because (as far as I can tell), SSLContext is thread-safe. Unfortunately its javadocs do not say anything explicitly regarding thread safety.