javascript: AES PrivateKey how to get it in js from c#

I have a problem :/.

I have a websocket server coded with c# and a website coded with (80%) js (angular).

I don't know how can I secure the communication :(.

I use fleck for my websocket server but I don't know what's the certificates (wss) and if i will use AES I don't know how can I get the private key for the client (website).

Thanxs you for your help and sorry for my bad english :/