The preventSilentAccess() method of the CredentialsContainer interface sets a flag that specifies whether automatic log in is allowed for future visits to the current origin, then returns an empty Promise. For example, you might call this, after a user signs out of a website to ensure that they aren't automatically signed in on the next site visit. Mediation varies by origin, and is an added check point of browser stored credentials, informing a user of an account login status. This method is typically called after a user signs out of a website, ensuring this user's login information is not automatically passed on the next site visit.
Earlier versions of the spec called this method requireUserMediation(). The Browser compatibility section has support details.