sasl_server_start() begins the authentication with the mechanism specified with mech. This
fails if the mechanism is not supported. SASL_OK is returned if the
authentication is complete and the user is
authenticated. SASL_CONTINUE is returned if one or more steps are
still required in the authentication. All other return values indicate
conn is the SASL context for this connection
mech is the mechanism name that the client requested
clientin is the client initial response, NULL if the protocol lacks support for
client-send-first or if the other end did not have an initial send. Note that
no initial client send is distinct from an initial send of a null string,
and the protocol MUST account for this difference.
clientinlen is the length of initial response
serverout is created by the plugin library. It is the initial server response to send to the client. This is allocated/freed by the library and it is the job of the client to send it over the network to the server. Also protocol specific encoding (such as base64 encoding) must needs to be done by the server.
serveroutlen is set to the length of initial server challenge