Add the auth authentication parameter to the handshake process

[Canees]

https://github.com/paullouisageneau/libdatachannel/blob/ed2fb2c73f872c166d2266b11842448db3171eb1/src/impl/websocket.cpp#L129

Hello, would you consider adding authentication parameters to the handshake?

These parameters are very suitable for verification.

[Canees]

@paullouisageneau @murat-dogan Do you have any good suggestions?