The reason Expensify does that is because they want/need access to the cookies from the login flow. The in app browser provides the hosting application access to those, but they can't access Safari's cookiejar. The modern way of doing it is to put the login in Safari (or iOS's dedicated "in app browser for logins") and then redirect to something like expensify://login_complete?token=xxxxxx, which pops back over to the app. This is mostly tech debt on Expensify's part, but it might not solve the Edge vs. Safari issue.