when a client connect to the node by websocket, the node will generate a challenge and send to the client
when the client get the challenge, it sign the challenge by its private key, and send setClient action to the node, node will check if it has field Signature
if have signature field, the node verify the signature by client public key.
if pass verification, keep the connection, else disconnect it.
Signed-off-by: billfort fxbao@hotmail.com