A bug exists in PHP that prevents users from connecting to a remote infrastructure using SSH with a passphrase. You are able to connect using the command line, but may encounter problems with the same key pair when connecting using PHP. This can also potentially be a problem if you’re using SSH tunneling for server-side applications.

The version of PHP that is making this connection (whether it’s running locally or on a remote infrastructure) needs the SSH2 PHP extension.

Here’s an example of some PHP you might use to try to connect to an Cloud Platform infrastructure:

<?php

   $conn_id = ssh2_connect("srv-NNNN.devcloud.hosting.acquia.com",22, array('hostkey'=>'ssh-rsa'));

   if (ssh2_auth_pubkey_file($conn_id, 'username','/Users/usename/.ssh/key.pub','/Users/username/.ssh/key','passphrase')) {
      echo "Public Key Authentication Successful\n";
      } else {
      die('Public Key Authentication Failed');
   }

?>

If the key.pub file requires a passphrase, the connection attempt can fail with this error:

PHP Warning:  ssh2_auth_pubkey_file(): Authentication failed for <username>
using public key: Callback returned error in <path_to_script>
line <line_number>

This is still an open bug with PHP. To work around this on Cloud Platform, create a public/private key pair without a passphrase. Then, add it to your Acquia profile using the Cloud Platform interface. You can then use the key, using ssh2_auth_pubkey_file() (as in the preceding example) without the optional passphrase parameter.