使用curl命令使用devise登录rails api

I have a simple web app built with rails using devise for user log in. At the moment a user can sign up, sign in and sign out, and make new posts when signed in. Eventually I plan to make this api consumable via a mobile app and my first step in understanding the process is to use a CURL command to log in. I am having some problems.I have a simple web app built with rails using