If you choose NemID as a login method and switch to MitID thorugh fallback function, can we as a service provider see that the customer did choose NemID as first option? (with information like SSN numbers etc.)
The final authentication or signing result will present itself as the method that the end user chose. If they clicked the fallback link in MitID and identified with NemID, the result will be presented as NemID, contain a NemID dataset and be logged as NemID.
You as a service provider will need to take the necessary steps to accept both results. For example, NemID will not populate the mitid.* claims, and MitID will return a UUID rather than PID.