Reference to all the PDO::MYSQL_* constants is available in MySQL's documentation for the driver here: https://dev.mysql.com/doc/connectors/en/apis-php-pdo-mysql.html
Such as the ones I was looking for PDO::MYSQL_ATTR_SSL_CA and PDO::MYSQL_ATTR_SSL_CAPATH which are not listed on this page.