Add new SQLite3 functions for password hash generation

[JavierJF]

This PR introduces two new SQLite3 functions:

• 'MYSQL_NATIVE_PASSWORD'
• 'CACHING_SHA2_PASSWORD'

These functions are accessible from the Admin interface, and allow generating MySQL compatible passwords:

• 'MYSQL_NATIVE_PASSWORD': Expects one argument, the desired user password and returns it's hashed version, using the SHA1 of the SHA1 as MySQL.

admin> SELECT MYSQL_NATIVE_PASSWORD('example_pass');
+-------------------------------------------+
| MYSQL_NATIVE_PASSWORD('example_pass')     |
+-------------------------------------------+
| *520BA5BE3924F1A0DB9941C4EA0911B19CBDE1A3 |
+-------------------------------------------+
1 row in set (0.00 sec)

• CACHING_SHA2_PASSWORD: Expects either one, or two arguments. The first argument is the password to hash and the second, and optional one, is the salt use for the hash generation. If no second argument is provided, the password will be generated using a randomly generated salt. Use with one argument:

admin> SELECT CACHING_SHA2_PASSWORD('example_pass');
+------------------------------------------------------------------------+
| CACHING_SHA2_PASSWORD('example_pass')                                  |
+------------------------------------------------------------------------+
| $A$005$Lpnj_Ps)C4q2hg;%       EISfOW43XEg7z7e3VScxZg6Qn1/WGKo8sT.k4Tb9mB1 |
+------------------------------------------------------------------------+
1 row in set (0.02 sec)

admin> SELECT HEX(CACHING_SHA2_PASSWORD('example_pass'));
+----------------------------------------------------------------------------------------------------------------------------------------------+
| HEX(CACHING_SHA2_PASSWORD('example_pass'))                                                                                                   |
+----------------------------------------------------------------------------------------------------------------------------------------------+
| 244124303035244B337D2B184A464C50195B2377463F790A193B4D4B307566385637646A5457692E646B6C765768734A5145765863555939684732566A624E6D464E4C317838 |
+----------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

The password should always be copied using the HEX format, otherwise characters could be escaped, because the has can contain characters may not be representable, see ProxySQL doc. With two parameters, a salt can be provided, this can be used to replicate MySQL passwords, without having the complete hash for them, only the used salt:

mysql> CREATE USER 'example_user'@'%' IDENTIFIED WITH 'caching_sha2_password' BY 'example_pass';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT user, HEX(authentication_string), HEX(SUBSTR(authentication_string, 8, 20)) AS salt FROM mysql.user WHERE user='example_user';
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------+
| user         | HEX(authentication_string)                                                                                                                   | salt                                     |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------+
| example_user | 24412430303524156B250133593C08146133655714470A700D203D7A646833593169655241513430396C3833464B7764377661755138586563446F4A63466454676367747737 | 156B250133593C08146133655714470A700D203D |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------+
1 row in set (0.00 sec)

Now in ProxySQL Admin:

admin> SELECT HEX(CACHING_SHA2_PASSWORD('example_pass', UNHEX('156B250133593C08146133655714470A700D203D')));
+----------------------------------------------------------------------------------------------------------------------------------------------+
| HEX(CACHING_SHA2_PASSWORD('example_pass', UNHEX('156B250133593C08146133655714470A700D203D')))                                                |
+----------------------------------------------------------------------------------------------------------------------------------------------+
| 24412430303524156B250133593C08146133655714470A700D203D7A646833593169655241513430396C3833464B7764377661755138586563446F4A63466454676367747737 |
+----------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)