SASL mechanisms can be provided from our implementations, or from Cyrus SASL. Our Cyrus SASL client implementation inspects the name of the requested mechanism, to figure out whether it should handle the request, or whether it should be delegated to the native implementation.

While we have a native PLAIN implementation, the mechanism factory will only make Cyrus instances. This means that on Community, PLAIN is always a viable mechanism. But on Enterprise, PLAIN in only viable if the correct Cyrus SASL plugin is installed.

We should always use the native PLAIN implementation, so that we don't have this conditional dependency.