Ionic Auth + external SQL database


Hey, I’m currently using the ionic auth-service with the basic-provider (email+password) for user management in my ionic2 project and it’s working fine!
But as a next step I need an (external) database for managing for example user tasks. Each user has his own tasks and should only be able to edit his own tasks. How can I authenticate that it’s the real user making the api-call? Of course I could submit the user-id in the POST/PUT and add it to the SQL-query, but it can always be manipulated, as the ID is not really secret, isn’t it?
Please give me a hint how I could solve this, thank you very much!