从PHP脚本使用客户端证书（无密码）连接到SMTP服务器并发送电子邮件

Question

I need to implement a script to send emails on behalf of an existing email server. The emails server supports only one way of authentication which is "Client Certificate Authentication". I only have an email address and a certificate to authenticate through my php script (no password), and send emails. and that is the only thing I know about the server :(.

I have not much idea about client certificate authentication, have searched over already but could not find any useful documents for the particular case.

Can some buddy pleas point me to the right direction ?

Answer 1

Good question. This is a bit of a guess, but I would expect that you need to disable normal auth and provide the client cert via the stream context options passed to the TLS connection.

I suggest these changes over a regular PHPMailer SMTP+STARTTLS connection:

$mail->SMTPSecure = 'tls';
$mail->Port = 587;
$mail->SMTPAuth = false;
$mail->SMTPOptions = [
    'ssl' => [
        'verify_peer'  => true,
        'local_cert' => '/path/to/client_cert_and_key.pem'
    ]
];

The local cert file should contain both the client private key and certificate in PEM format.

Look at this example for more complete code that uses SSL stream context options.