Add support for secure DB connections to PDO / mysqli

[hypertextranch]

With the advent of database as a service cloud providers like Amazon RDS, ClearDB, etc. it would be good to have the option of connecting to MySQL over SSL so database credentials are not sent in clear text over the internet.

SSL support for mysql_connect was added in #19324 however with the impending update (in 3.6?) to PDO / mysql_* for database connections #21663 we will no longer have this option. (By the way I'm not sure the MYSQL_CLIENT_SSL flag in mysql_connect() ever worked as there's nowhere to specify CA/key/cert file paths)

I propose we patch #21663 to construct SSL enabled DB connections with mysqli::ssl_set() and PDO driver options flags when all of the following constants are defined:

• DB_SSL_KEY
• DB_SSL_CERT
• DB_SSL_CA

References:
​http://www.php.net/manual/en/mysqli.ssl-set.php
​http://php.net/manual/en/ref.pdo-mysql.php

[rmccue]

Replying to hypertextranch:

however with the impending update (in 3.6?) to PDO / mysql_* for database connections #21663

This won't be landing in 3.6. I'd recommend that this suggestion stay as part of that ticket for now.

[SergeyBiryukov]

Duplicate of #21663.