Magento Force Customer Login With Password

magento-auth-customer-pass

Mage::app("default");

// Set the variables that we care about.  
$storeId = 1;
$username = 'their.email@their.domain.com';
$password = 'theirpassword'; 
      
try{   
    $authenticated = Mage::getModel('customer/customer')
        ->setWebsiteId($storeId)
        ->authenticate($username, $password);  
} catch ( Exception $e ) {  
    $authenticated = false;  
}

// Do something depending on whether $authenticated is truthy