I noticed that Pinterest app on my iPad (iPad 4, iOS 10.3.3) keeps log in credentials after delete/reinstall. As a iOS user and not a programmer, I managed to find out from some posts I could understand, that iOS apps can keep data between instalations on Keychain, iCloud or Dropbox.
Pinterest never asked for access on iCloud, Dropbox or similar cloud storage. I suppose it stocks login data in Keychain and do not delete it when uninstalling.
Please help me to understand: is it a local keychain that iOS apps can use, different from iCloud Keychain? Is it so that only the iCloud Keychain could be user enabled / disabled, the local keychain beeing an always on iOS feature that every app developer can use whithout requesting user permission?
I ask this because I never enabled iCloud Keychain on any of my iOS devices. Or does Pinterest app use other iOS feature that I don't read about to retain log in credentials?