We need to make sure that when sending plugin supplied data to the client they are not considered a special out-of-band command, like e.g.

ERR_Packet, Protocol::AuthSwitchRequest: or OK_Packet. To avoid this the server will send all plugin data packets "wrapped" in a command \1. Note that the client will continue sending its replies unrwapped: Protocol::AuthSwitchResponse:

Payload
Type	Name	Description
int<1>	0x01	status tag
string<EOF>	authentication method data	Extra authentication data beyond the initial challenge

See also: wrap_plguin_data_into_proper_command, server_mpvio_write_packet, client_mpvio_read_packet