It is sometimes handy to know which authentication methods an ssh server supports. This may be useful if you want to enable or disable certain authentication method. Here is how you can find it using command line.
Using ssh with PreferredAuthentications=none
Simply do an ssh to server and ssh will print supported methods:
ssh -o PreferredAuthentications=none localhost Permission denied (publickey).
For detailed information you can also look at RFC – The Secure Shell (SSH) Authentication Protocol