I am newbie to REST api but I have done many projects with Codeigniter . I am having a problem API because I would like to improve performance for API particularly user authentication . My api is especially designed for android app . My current authentication api flow is as follow . Mobile user login to app by entering username and password . That is sent to the api and api validates username and password against database . Then return success message , ID and so on . But for the second api request , for example ,user want to retrieve somethings else from database , I have to validate against database then the new request is served . So every time , I have to validate username and password against database . Is there anyway to maintain user login state after user is logged in for the first time. I am using Codeigniter version 2.2.1 .