We're running a PHP 5.4 application on Server 2008 R2. We would like to connect to a SQL Server 2008 database, on a separate server, using Windows authentication (must be Windows authentication--the DB admins won't let us connect any other way). I have downloaded the SQL Server drivers for PHP and installed them. IIS is configured for Windows authentication, and anonymous authentication has been disabled. $_SERVER['AUTH_USER'] reports our currently logged on Windows account. In php.ini, we have set fastcgi.impersonate = 1.

When we setup a connection using the following code from Microsoft:

$serverName = "sqlserver\sqlserver";
$connectionInfo = array( "Database"=>"some_db");

/* Connect using Windows Authentication. */
$conn = sqlsrv_connect( $serverName, $connectionInfo);
if( $conn === false )
{
     echo "Unable to connect.</br>";
     die( print_r( sqlsrv_errors(), true));
}

We are presented with the following error message:

Unable to connect.
Array ( [0] => Array ( [0] => 28000 [SQLSTATE] => 28000 [1] => 18456 [code] => 18456 [2] => [Microsoft][SQL Server Native Client 11.0][SQL Server]Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'. [message] => [Microsoft][SQL Server Native Client 11.0][SQL Server]Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'. )

Is it possible to connect to SQL Server 2008 via PHP using Windows authentication? Are there any additional required settings we need to make on IIS, SQL Server, or any other component (like a domain controller)?