Open Regedit and do the following:
- HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, create a DWORD value named EnableADAL and set it to zero.
- Under the same registry key, create a DWORD value named DisableADALatopWAMOverride and set it to 1
- Reboot
After reboot it shouldn't ask for a password again.