I have developed 2 apps that use custom tabs for login. I want to achieve single sign-on where I'm relying on the identity provider (server) to detect the same session (stored in custom tabs cookies) and automatically authenticate the user.

Application Version (from "Chrome Settings > About Chrome"): Chrome 60.0.3112.116
Android Build Number (from "Android Settings > About Phone/Tablet"): 7.0
Device: Samsung Galaxy S8+

Steps to reproduce:
1. Open App#1 > click sign in > get asked for your credentials.
2. Open App#2 > click sign in.

Observed behavior: 
I'm only getting automatically signed in if I open app#2 within 15~20 min after opening app#1. When I wait longer than that, app#2 will ask for sign in credentials again. 

Expected behavior: 
App#2 should never ask for credentials and get automatically signed in using the session cookie in its custom tab.

Frequency: 
100% 

Additional comments: 
Does that mean that the custom tab cookies expire at some point?
To my understanding cookies in the chrome browser and all the custom tabs on the device remain forever (or until manually cleared), which means that every app on the same device that uses the same IdP should call the authentication request using the same session ID, thus getting recognized and automatically signed in by the server. 
Is my understanding correct? anything I'm missing?.

Thanks.