Add 'switching_auth_sent' to 'PROXYSQL INTERNAL SESSION'

Improved observability for auth switch performed during authentication.
The new field 'switching_auth_sent' is only updated when an actual auth
switch requested to the client.

include/MySQL_Data_Stream.h

@@ -159,6 +159,8 @@ class MySQL_Data_Stream
 
 	int switching_auth_stage;
 	enum proxysql_auth_plugins switching_auth_type;
+	// Updated **only** when an 'auth_switch' has been sent to client
+	enum proxysql_auth_plugins switching_auth_sent;
 	int auth_in_progress; // if 0 , no authentication is in progress. Any value greater than 0 depends from the implementation
 	unsigned int tmp_charset;
 

lib/MySQL_Protocol.cpp

@@ -1207,6 +1207,8 @@ bool MySQL_Protocol::generate_pkt_auth_switch_request(bool send, void **ptr, uns
 		(*myds)->DSS=STATE_SERVER_HANDSHAKE;
 		(*myds)->sess->status=CONNECTING_CLIENT;
 	}
+	(*myds)->switching_auth_sent = (*myds)->switching_auth_type;
+
 	if (len) { *len=size; }
 	if (ptr) { *ptr=(void *)_ptr; }
 #ifdef DEBUG

lib/MySQL_Session.cpp

@@ -1163,6 +1163,7 @@ void MySQL_Session::generate_proxysql_internal_session_json(json &j) {
 			}
 		}
 		j["client"]["DSS"] = client_myds->DSS;
+		j["client"]["switching_auth_sent"] = client_myds->switching_auth_sent;
 		j["client"]["switching_auth_type"] = client_myds->switching_auth_type;
 		j["client"]["prot"]["sent_auth_plugin_id"] = client_myds->myprot.sent_auth_plugin_id;
 		j["client"]["prot"]["auth_plugin_id"] = client_myds->myprot.auth_plugin_id;

lib/mysql_data_stream.cpp

@@ -306,6 +306,7 @@ MySQL_Data_Stream::MySQL_Data_Stream() {
 	encrypted=false;
 	switching_auth_stage = 0;
 	switching_auth_type = AUTH_UNKNOWN_PLUGIN;
+	switching_auth_sent = AUTH_UNKNOWN_PLUGIN;
 	auth_in_progress = 0;
 	x509_subject_alt_name=NULL;
 	ssl=NULL;