login without a password

Nope..didn't find a solution, sorry..stiill interested though!

Hi Jeff,
Did you find a solution in the end? Please post it back to the forum so that it's not a dead end for people googling.

We were having the same issue on one of our sites...
Wanted to allow people to switch users without having to remember their password.

Here's what I did:

// So you want to log a user in without a password? 
// all you need is the username:

// Get the (user) name of the user you are signing in. 
// Either from $_POST['name'] or $form['name'] 
// depending on how you're crafting the login form.
$name = check_plain($_POST['name']);          

// user_load() by name         
$user = user_load(array('name' => $name));    

// get the current password hash from the user object 
// and store it in a variable. (we will need it later)      
$originalpass = $user->pass;                                

//  a temporary password for the user we are going to log in! 
$newpass = 'SomeRandomC0mpl3xString';         
$newhash  = md5($newpass);                       
// provided your drupal is not using "salt" or encryption this will work fine.          

// SQL query to set the user's password to the Temporary one
$update = "UPDATE users SET pass = '%s' WHERE name='%s';";  
$updated = db_query($update, $newpass, $name);              

// So at this stage your user has users.pass = $newpass   

// set the user login parameters
$params = array(  
			'name'=>$name,
			'pass'=>$newpass,
			'status'=>1
		);	

// login as this user  using the  standard drupal method 
// for user authentication supplying the above parameters. 

$account = user_authenticate( $params ); 
// note: D5/D7 is slightly different. see below.                              

// once we have the $account object we need to re-set 
// the password back to what ever it was before this login

// SQL query to set the user's password to the Temporary one
$reset = "UPDATE users SET pass = '%s' WHERE name='%s';";  

// Run the query           
$updated = db_query($update, $originalpass, $name);                      

return $account;

Notes:
user_authenticate - http://api.drupal.org/api/drupal/modules--user--user.module/function/use...
user_load - http://api.drupal.org/api/drupal/modules--user--user.module/function/use...

if you prefer to log users in using email address add it to $params array: 'mail'=>$email, for our purposes stick with $name

This code can easily be turned into a function or method as required.
You just need to know that you are submitting a (user) name as the parameter.
or you could even allow a name or email by having:

function drupal_login_no_password($name = NULL, $mail = NULL)
{
// place the above code in here and write a quick switch / case to check which variable is set so you can feed it to the user_load and user_authenticate methods. :-)
}

Let me know if this answers your quest(ion)
If not, be specific with requirements.

Cheers.
p.s. I know the above code is very crude and inelegant but it works.