PHP - authenticate and authorize using AS400 profile

I've been working on a PHP function that: (1) authenticates a user by
connecting to the AS400, and (2) authorizes a user based on information
from the user profile. I've included the code at the end of this post.



The code works. My question has to do with accepting the user name and
password from the $_POST array.



I know the mantra is "never trust user input." However, we use long
passwords, and we encourage users to make up passwords that include
special characters. Do I need to scrub the input at all, since I'm only
using it to establish a connection and set a $_SESSION variable? Should
I scrub certain characters (and tell users they can't include those
characters in their passwords)? If so, which characters?



Thanks,

Kelly



Note: the script below assumes users are authorized to access an
application if they belong to the *SECOFR user class or they belong a
supplemental group called MYGROUP.



function validateUser()

{

//Step 1: Authenticate the user by connecting to the AS400.

$username=$_POST["user"];

$password=$_POST["password"];

$conn = i5_connect("myas400",$username,$password);

if (!$conn)

{

$result = "Invalid username or password.";

}

else

{

//Step 2. Authorize the user by checking profile information;

$rtvusrprf = (i5_command("rtvusrprf",

array("usrprf"=>"*CURRENT"),

array("usrcls"=>"usrcls","supgrpprf"=>"supgrpprf"),

$conn));

if (!$rtvusrprf)

{

$result = "Authorization error.";

}

else

{

if ($usrcls == "*SECOFR")

{

$_SESSION["user"] = $username;

$result = "Thank you for signing in.";

}

else

{

$supgrps = str_split($supgrpprf, 10);

if (in_array("MYGROUP", $supgrps))

{

$_SESSION["user"] = $username;

$result = "Thank you for signing in.";

}

else

{

$result = "Not authorized for this application.";

}

}

}

//Step 3. Close connection. Use the NOBODY profile for better
performance.

i5_close($conn);

}

return $result;

}