Multifactor resolver always uses default instance #12265
Description
Description
In FIRMultFactorResolver defining an instance that is not default does not allow one to finish mfa sign in because it always finalizes with the default instance.
I expected the mfa to finalize, but what actually happened was I got a "user does not belong to this project" error.
Reproducing the issue
Initialize the default instance of FIRAuth with the info.plist to be some firebase project.
Implement a sign in flow with a different instance and catch the multifactor resolver from it's authentication error.
When you try to finalize the sign in with, it tries to use the wrong instance, which can be verified with a breakpoint or by using
a proxy and observing the wrong api key being used.
Firebase SDK Version
10.9
Xcode Version
14.3
Installation Method
CocoaPods
Firebase Product(s)
Authentication, Messaging
Targeted Platforms
iOS
Relevant Log Output
No response
If using Swift Package Manager, the project's Package.resolved
No response
If using CocoaPods, the project's Podfile.lock
No response