Basically, you need to put user's public key to the server and asociate this public key with a user account. When connecting from a client side, you need to use private key to authenticate.
To request clients to authenticate using password and public key in Buru SFTP Server, you have to set both password and public key authentication method to
required. It can be done in Web Administration page, section users, then pick up a user who should use password and public key together. Then choose required for both authentication method. In public key authentication section you have to choose a public key file for which the client possess a private key and will use to authenticate.
So you need to create private/public key pair, for example using ssh-keygen command line tool. Just run
ssh-keygen from your command promp. Then follow the instruction the program gives you. Use something like
C:\MyKeys\BuruClientKey, then in
C:\MyKeys you will find both private (file without an extension) and public key (file with .pub extension). When enabling public key authentication in Buru SFTP Server Web Administration, choose this .pub key file as a public key.
On the client side, you have to prove that the public key on the server is yours by using private key part of the key pair. For example, WinSCP client can authenticate using both password and private key.
Please make sure that a public key is copied to the server and is associated with correct user account. Then make sure when connecting from a client it will use proper private key that correspond with the public key on the server.