Creates a new random key for a WebSocket handshake.
Returns the base64-encoded random key.
Use this method to create a new value for the Sec-WebSocket-Key header field. The WebSocket key is a nonce consisting of a randomly selected 16-byte value that has been base64-encoded, and is used in the server's handshake to indicate the acceptance of the connection. The unique key has to be generated for each new connection.