In an OAuth flow, we redirect to Auth0 with a hint to log in the user. When testing with multiple users, after the first login, Auth0 skips the login screen and uses the current cookie. We would like to be able to test our application with multiple users in one browser or even different windows but can not.
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You can force a login prompt with prompt=login param. This should allow you to test multiple logins within the same session without the automatic silent login. More info: Force Reauthentication in OIDC
Otherwise, you can clear the cookie, use an incognito window, or a different browser.