fix @@external_user variable

mysql-test/r/plugin_auth.result

@@ -224,7 +224,7 @@ NULL
 # in connection plug_con
 SELECT @@LOCAL.external_user;
 @@LOCAL.external_user
-'plug'@'%'
+plug_dest
 # in connection default
 ## cleanup
 DROP USER plug;

mysql-test/r/plugin_auth_qa_2.result

@@ -44,7 +44,7 @@ SELECT @@external_user;
 NULL
 exec MYSQL -h localhost -P MASTER_MYPORT -u qa_test_2_user --password=qa_test_2_dest test_user_db -e "SELECT current_user(),user(),@@local.proxy_user,@@local.external_user;" 2>&1
 current_user()	user()	@@local.proxy_user	@@local.external_user
-authenticated_as@%	user_name@localhost	'qa_test_2_user'@'%'	'qa_test_2_user'@'%'
+authenticated_as@%	user_name@localhost	'qa_test_2_user'@'%'	externaluser
 SELECT user,plugin,authentication_string FROM mysql.user WHERE user != 'root';
 user	plugin	authentication_string
 authenticated_as		
@@ -60,7 +60,7 @@ GRANT ALL PRIVILEGES ON test_user_db.* TO qa_test_3_dest identified by 'dest_pas
 GRANT PROXY ON qa_test_3_dest TO qa_test_3_user;
 exec MYSQL -h localhost -P MASTER_MYPORT -u qa_test_3_user --password=qa_test_3_dest test_user_db -e "SELECT current_user(),user(),@@local.proxy_user,@@local.external_user;" 2>&1
 current_user()	user()	@@local.proxy_user	@@local.external_user
-qa_test_3_dest@%	qa_test_3_user@localhost	'qa_test_3_user'@'%'	'qa_test_3_user'@'%'
+qa_test_3_dest@%	qa_test_3_user@localhost	'qa_test_3_user'@'%'	qa_test_3_dest
 DROP USER qa_test_3_user;
 DROP USER qa_test_3_dest;
 === Assign too low values for *length, which should have no effect ====
@@ -70,7 +70,7 @@ GRANT ALL PRIVILEGES ON test_user_db.* TO qa_test_4_dest identified by 'dest_pas
 GRANT PROXY ON qa_test_4_dest TO qa_test_4_user;
 exec MYSQL -h localhost -P MASTER_MYPORT -u qa_test_4_user --password=qa_test_4_dest test_user_db -e "SELECT current_user(),user(),@@local.proxy_user,@@local.external_user;" 2>&1
 current_user()	user()	@@local.proxy_user	@@local.external_user
-qa_test_4_dest@%	qa_test_4_user@localhost	'qa_test_4_user'@'%'	'qa_test_4_user'@'%'
+qa_test_4_dest@%	qa_test_4_user@localhost	'qa_test_4_user'@'%'	qa_test_4_dest
 DROP USER qa_test_4_user;
 DROP USER qa_test_4_dest;
 === Assign empty string especially to authenticated_as (in plugin) ====

mysql-test/r/plugin_auth_qa_3.result

@@ -4,7 +4,7 @@ GRANT ALL PRIVILEGES ON test_user_db.* TO qa_test_11_dest identified by 'dest_pa
 GRANT PROXY ON qa_test_11_dest TO qa_test_11_user;
 exec MYSQL --default_auth=qa_auth_client -h localhost -P MASTER_MYPORT -u qa_test_11_user --password=qa_test_11_dest test_user_db -e "SELECT current_user(),user(),@@local.proxy_user,@@local.external_user;" 2>&1
 current_user()	user()	@@local.proxy_user	@@local.external_user
-qa_test_11_dest@%	qa_test_11_user@localhost	'qa_test_11_user'@'%'	'qa_test_11_user'@'%'
+qa_test_11_dest@%	qa_test_11_user@localhost	'qa_test_11_user'@'%'	NULL
 exec MYSQL --default_auth=qa_auth_client -h localhost -P MASTER_MYPORT -u qa_test_2_user --password=qa_test_11_dest test_user_db -e "SELECT current_user(),user(),@@local.proxy_user,@@local.external_user;" 2>&1
 ERROR 1045 (28000): Access denied for user 'qa_test_2_user'@'localhost' (using password: NO)
 DROP USER qa_test_11_user, qa_test_11_dest;

sql/sys_vars.h

@@ -547,8 +547,7 @@ class Sys_var_external_user : public Sys_var_proxy_user
 protected:
   virtual uchar *session_value_ptr(THD *thd, LEX_STRING *base)
   {
-    return thd->security_ctx->proxy_user[0] ?
-      (uchar *) &(thd->security_ctx->proxy_user[0]) : NULL;
+    return (uchar*)thd->security_ctx->external_user;
   }
 };