I want to be able to test if a user is logged by passing the user's email address using the SOAP API v2.
Would it be possible to create my own API call for that: http://www.magentocommerce.com/api/soap/create_your_own_api.html
Yes you can create your own API that would do this by using loadByEmail from the core Customer model.
Also, I guess I could use a filter on the email. How would I modify this filter to do that?
$client = new SoapClient('http://magentohost/api/v2_soap/?wsdl'); // If some stuff requires api authentification, // then get a session token $session = $client->login('apiUser', 'apiKey'); $complexFilter = array( 'complex_filter' => array( array( 'key' => 'group_id', 'value' => array('key' => 'in', 'value' => '1,3') ) ) ); $result = $client->customerCustomerList($session, $complexFilter); var_dump ($result);