Shared cookie jar and permissions model so users don't have to log in to sites they are already connected to, or re-grant permissions they have already granted.
Chrome Custom Tabs
is the Chrome
browser (via the Chrome service and custom Intents) and thus the cache, cookies, etc.. are shared (actually the same).
The answer is no, you can not programmatically clear the data of Chrome.
Note: Right now there is no support of creating an Incognito-based Custom Tab
I would issue the user a transient/session cookie so it does not get persisted if you wish to forced a re-login on the start of every new session.