Q:

Use case of increased https security in JAVA

I am writing an application that should ensure secured connection between two parties (call them Client and Server).
Server should restrict which clients can connect using https. For this purpose, server will issue a certain number of certificates that will be checked when a client tries to connect. If the certificate that the client is using is not in trusted list, connection would not be established. 
This certificate should be distributed using some kind of usb device. So when Client using my application tries to get something from server using https, application should read that certificate from usb device and USE IT to establish https connection. Private key should be kept secret on the device at all times.
So far I managed to create local keystores on client and server (JKS), add them to each other trusted list and use them to achieve proper connection.
My question is:  can client certificates be issued by a server and transported to clients, all together with private key required for https connection? I dont want any data or keystore to be created on the client machine, everything required for establishing https connection should be on that device. Device could have some procedures and api to help this process and ensure secrecy of private key.
Any help will be greatly appreciated :)

A:

can client certificates be issued by a server and transported to
  clients, all together with private key required for https connection?

Technically, they can, but you're going to have to authenticate that connection by some other means if you want to make sure that private key only gets to its intended user. As far as your overall scheme is concerned, this doesn't really help. In addition by sending the private key as data to the client, they may be able to extract it one way or another.
If you can physically send a USB device, you can use a hardware cryptographic token that supports PKCS#11. Such tokens tend to have options to store a private key in a way in can't be extracted (it can only be used with the device). They tend to come in to forms: as a smart card (in which case you need a reader) or as a USB token (it looks like a memory stick, but it's not). Depending on the model, the USB token can in fact be a smart card with an embedded reader.
Java supports PKCS#11 keystores, so if this token comes with a PKCS#11 driver/library, it could be used from Java.

