How do I make it always force the user to enter their login credentials instead of assuming them?

[shakked]

I'm building a tool where a user would want to authenticate multiple Instagram accounts into the application. The problem I run into is if the user has already authenticated one and I initiate the OAuth dialogue again, the OAuth assumes that I want the access token of the user already logged in.

I have an iOS app that is similar and the way to avoid this is clear all the cookies of the Safari browser.