MDEV-22974: mysql_native_password make "invalid" valid

Per b9f3f06857ac, mysql_system_tables_data.sql creates
a mysql_native_password with a salted hash of "invalid" so that `set password`
will detect a native password can be applied:.

SHOW CREATE USER; diligently uses this value in its output
generating the SQL:

   MariaDB [(none)]> show create user;

   +---------------------------------------------------------------------------------------------------+
   | CREATE USER for dan@localhost                                                                     |
   +---------------------------------------------------------------------------------------------------+
   | CREATE USER `dan`@`localhost` IDENTIFIED VIA mysql_native_password USING 'invalid' OR unix_socket |
   +---------------------------------------------------------------------------------------------------+

Attempting to execute this before this patch results in:

  MariaDB [(none)]>  CREATE USER `dan2`@`localhost` IDENTIFIED VIA mysql_native_password USING 'invalid' OR unix_socket;
  ERROR 1372 (HY000): Password hash should be a 41-digit hexadecimal number

As such, deep the implementation of mysql_native_password we make "invalid" valid (pun intended)
such that the above create user will succeed. We do this by storing
"*THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE" (credit: Oracle MySQL), that is of an INCORRECT
length for a scramble.

In native_password_authenticate we check the length of this cached value
and immediately fail if it is anything other than the scramble length.

native_password_get_salt is only called in the context of set_user_salt, so all setting of native
passwords to hashed content of 'invalid', quite literally create an invalid password.

So other forms of "invalid" are valid SQL in creating invalid passwords:

   MariaDB [(none)]> set password = 'invalid';
   Query OK, 0 rows affected (0.001 sec)

   MariaDB [(none)]> alter user dan@localhost IDENTIFIED BY PASSWORD 'invalid';
   Query OK, 0 rows affected (0.000 sec)

closes #1628

Reviewer: serg@mariadb.com

1 files changed, 4 insertions, 0 deletions

diff --git a/mysql-test/main/alter_user.result b/mysql-test/main/alter_user.result
index 6f88f0311bd..0dcec5835b7 100644
--- a/mysql-test/main/alter_user.result
+++ b/mysql-test/main/alter_user.result
@@ -61,6 +61,10 @@ alter user foo identified by password '*88C89BE093D4ECF72D039F62EBB7477EA1FD4D63
 select * from mysql.user where user = 'foo';
 Host	User	Password	Select_priv	Insert_priv	Update_priv	Delete_priv	Create_priv	Drop_priv	Reload_priv	Shutdown_priv	Process_priv	File_priv	Grant_priv	References_priv	Index_priv	Alter_priv	Show_db_priv	Super_priv	Create_tmp_table_priv	Lock_tables_priv	Execute_priv	Repl_slave_priv	Repl_client_priv	Create_view_priv	Show_view_priv	Create_routine_priv	Alter_routine_priv	Create_user_priv	Event_priv	Trigger_priv	Create_tablespace_priv	Delete_history_priv	ssl_type	ssl_cipher	x509_issuer	x509_subject	max_questions	max_updates	max_connections	max_user_connections	plugin	authentication_string	password_expired	is_role	default_role	max_statement_time
 %	foo	*88C89BE093D4ECF72D039F62EBB7477EA1FD4D63	N	N	N	N	N	N	N	N	N	N	N	N	N	N	N	Y	N	N	N	N	N	N	N	N	N	Y	N	N	N	N					0	0	0	0	mysql_native_password	*88C89BE093D4ECF72D039F62EBB7477EA1FD4D63	N	N		0.000000
+alter user foo identified by password 'invalid';
+select * from mysql.user where user = 'foo';
+Host	User	Password	Select_priv	Insert_priv	Update_priv	Delete_priv	Create_priv	Drop_priv	Reload_priv	Shutdown_priv	Process_priv	File_priv	Grant_priv	References_priv	Index_priv	Alter_priv	Show_db_priv	Super_priv	Create_tmp_table_priv	Lock_tables_priv	Execute_priv	Repl_slave_priv	Repl_client_priv	Create_view_priv	Show_view_priv	Create_routine_priv	Alter_routine_priv	Create_user_priv	Event_priv	Trigger_priv	Create_tablespace_priv	Delete_history_priv	ssl_type	ssl_cipher	x509_issuer	x509_subject	max_questions	max_updates	max_connections	max_user_connections	plugin	authentication_string	password_expired	is_role	default_role	max_statement_time
+%	foo	invalid	N	N	N	N	N	N	N	N	N	N	N	N	N	N	N	Y	N	N	N	N	N	N	N	N	N	Y	N	N	N	N					0	0	0	0	mysql_native_password	invalid	N	N		0.000000
 alter user foo identified with 'somecoolplugin';
 ERROR HY000: Operation ALTER USER failed for 'foo'@'%'
 show warnings;