Testflight review with 3rd party sign in

I recently submitted my app for test flight review, but in order to use my app, a user must sign in to a 3rd party app in my app (it's a smaller company, not google or anything), so I am thinking my app will get rejected. I saw the option to provide a sign in, but this third party requires 2fa, so that doesn't exactly work. I am wondering what the best workaround for this would be. My initial thought is to add in some code where if a user puts something like "skip" for the sign-in username then they can pass the login page, but that'll limit a lot of other functionality in the app. Has anyone else ever dealt with this before or have any ideas? Will my skip idea allow for the app to be approved?

Testflight review with 3rd party sign in
 
 
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