Bahaa

@chwe Sorry if this response is late, the official guide from Armbian based on "nmtui-connect" is robust and does the job for connecting but it needs user interaction, on the other hand, the tool from @botfap "https://github.com/botfap/armbian-image-config" is for pre-configuring an image, what I really need is a robust tool to configure WiFi non-interactively, after the images is burnt (to be used in a bash script for instance), since I don't know WiFi SSID/credentials in advance.  

@botfap made an initial push to restructure network configuration prior to first boot. I didn't test it on my own yet but I assume the wifi part should work and perfectly fit for your needs.
https://github.com/botfap/armbian-image-config
quite sure he's happy to get some response from people actually used it.  You might give it a try? 

http://docs.armbian.com/User-Guide_Getting-Started/#how-to-connect-to-wireless
per default, wifi is handled by NetworkManager. It may overwrite your credentials which then messes up.