Authentication issue in SMP from Windows AD (Active Directory)

Hello Gurus,

Current we are implementing SMP platform Native mobile app. I required your advise and suggestions for below scenario :

Current design :

Have ECC (Installed in different box) and NW (installed in different box) trusted RFC connection maintained between ECC & NW to consume ODATA services.

1) Our mobile app will authenticate through windows AD server. (user maintained / created as "MobileUser1" in AD and ECC server) *User id is same in both the servers

2) Is it mandatory to maintain the same user "MobileUser1"  in (NW server) ? to access for creating the orders, pull / sync the data

3) If we maintain "Mobileuser1" in NW server then how can we handle if AD user password changes then it's mandatory to change and create the same password in NW & ECC??

Any Help will Appreciated.

Thanks in Advance.

Regards

PavanG