Need a data access context of currently logged in user

Hi.I am looking for the best way to obtain currently logged user details, the most desirable is to get all of the business unit data assignments that user has. Need to create a simple customization based on the data access of currently logged in user. Is there any easy way to do that from the context of we need to use soap/rest apis to get those details?Maybe the EL expression? If APIs must be used is there any way to use session cookies to authorize the rest/soap request?Regards,Patryk