mysql  Ver 14.14 Distrib 5.7.21, for Linux (x86_64) using  EditLine wrapper

Connection id:      9
Current database:
Current user:       test@db.test.com
SSL:            Cipher in use is DHE-RSA-AES256-SHA
Current pager:      stdout
Using outfile:      ''
Using delimiter:    ;
Server version:     5.7.21-0ubuntu0.16.04.1 (Ubuntu)
Protocol version:   10
Connection:     0.0.0.0 via TCP/IP
Server characterset:    utf8mb4
Db     characterset:    utf8mb4
Client characterset:    utf8mb4
Conn.  characterset:    utf8mb4
TCP port:       3306
Uptime:         3 days 4 hours 53 min 35 sec

Threads: 1  Questions: 17  Slow queries: 0  Opens: 107  Flush tables: 1  Open tables: 26  Queries per second avg: 0.000

+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| have_openssl  | YES             |
| have_ssl      | YES             |
| ssl_ca        | ca.pem          |
| ssl_capath    |                 |
| ssl_cert      | server-cert.pem |
| ssl_cipher    |                 |
| ssl_crl       |                 |
| ssl_crlpath   |                 |
| ssl_key       | server-key.pem  |
+---------------+-----------------+

+-------------------------------------------------------------+
| Grants for test@0.0.0.0                             |
+-------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'test'@'0.0.0.0'              |
| GRANT SELECT ON `testDB`.* TO 'test'@'0.0.0.0' |
+-------------------------------------------------------------+

+--------------------------+------------------------+
| Variable_name            | Value                  |
+--------------------------+------------------------+
| character_set_client     | utf8mb4                |
| character_set_connection | utf8mb4                |
| character_set_database   | utf8mb4                |
| character_set_filesystem | binary                 |
| character_set_results    | utf8mb4                |
| character_set_server     | utf8mb4                |
| character_set_system     | utf8                   |
| collation_connection     | utf8mb4_unicode_520_ci |
| collation_database       | utf8mb4_unicode_520_ci |
| collation_server         | utf8mb4_unicode_520_ci |
+--------------------------+------------------------+

+------------------+-------------+-----------------------+----------+
| user             | host        | plugin                | ssl_type |
+------------------+-------------+-----------------------+----------+
| test             | 0.0.0.0     | sha256_password       | X509     |
+------------------+-------------+-----------------------+----------+

apache@web:~$ ls -al /etc/mysql-client
total 20
drwxr-xr-x  2 root root 4096 Mar 24 02:30 .
drwxr-xr-x 99 root root 4096 Mar 30 20:04 ..
-r-xr-xr-x  1 root root 1107 Mar 24 02:30 ca.pem
-r-xr-xr-x  1 root root 1107 Mar 24 02:30 client-cert.pem
-r-xr-xr-x  1 root root 1679 Mar 24 02:30 client-key.pem

$dsn = 'mysql:host=db.test.com;port=3306;dbname=testDB;charset=utf8mb4';
$dbuser = 'test';
$dbpass = 'sha256-hash';

$dboptions = array (
    PDO::MYSQL_ATTR_SSL_KEY    =>'/etc/mysql-client/client-key.pem',
    PDO::MYSQL_ATTR_SSL_CERT   =>'/etc/mysql-client/client-cert.pem',
    PDO::MYSQL_ATTR_SSL_CA     =>'/etc/mysql-client/ca.pem',
    PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT => false
);

    try {
        $conn = new PDO($dsn,$dbuser,$dbpass,$dboptions);
        if($conn){
                echo "Connection established";
        }
    } catch (PDOException $e) {
        echo 'Connection failed: ' . $e->getMessage();
    }

Connection to 0.0.0.0 3306 port [tcp/mysql] succeeded!

apache@web:~$ php -f test.php
Connection failed: SQLSTATE[HY000] [2002]