If you have your Android device with Kodi installed on it, you might want to
add remote folder using ssh/sftp protocol.
Since it's a bad security practice setup a ssh access allowing to log in using a
password instead of the ssh key, the setup should be done by using such file.
If you ever done this before in an OS as GNU/Linux or MacOS you'll be already familiar with the process and concepts as ssh, public/private keys, etc. If that's not your case, I recommend you to check the previous link.
The problem comes with Android devices is that there's no such idea as home folder
(~/ or /home/${USER}) and therefore, your ssh key should be placed somewhere else.
In the official documentation it's not specified what should the ssh key be placed,
but, in the official forum from Kodi, @mariuscampan gives the key to the solution.
The ssh key has to be placed in the following path:
/sdcard/Android/data/org.xbmc.kodi/files/.ssh
It's quite probable that you will need to create the .ssh folder.
Once your key is in there, nothing else needs to be done, you can add your
remote/network folder in your Kodi app.
Kodi wiil automatically use the file /sdcard/Android/data/org.xbmc.kodi/files/.ssh/id_rsa.
In order to create the .ssh folder and transfer the key, I've personally used
ES File Explorer app since it was the first one I found that allowed to manipulate
hidden folder. The free version it's quite bloated with ads and crappy background
jobs, so, I would use it just for this purpose and remove from the device.