If you use the app, you will notice that you have to sign in each time. A common question is why does the app make you sign in each time. While it is convenient to have the app sign you in automatically, it does come with a security risk.
The one reason why you have to sign in each time is because of security. If someone were to get a hold of your phone and open the app, they would be able to access your account automatically, if the app doesn't make you sign in each time. They would be able to access your account because the app would be storing your username and password, which the app currently does not do. So all a hacker, or someone with malicious intent, would have to do is tap on the app and all your PHI/records are available to them. To protect your information, the app will not store your login information and will make you sign in each time to authenticate that it's you signing in.
Another reason, more technical, why you have to sign in each time is because of the access token. The access token has a short lifetime. The token is only active while you are in the account. Once you sign out, that token expires, which is why you have to sign in again. And since the app does not store the token for an unlimited lifetime, you will be prompted each time to enter your login information or your mobile passcode.