Is there a way to list all available SSH authentication methods for the local host using command line? Basically, I want to see the same list which the server would announce when trying to connect from a (remote) client.
Note: I do not want to search through /etc/ssh/sshd_config, as this will require too much understanding of which authentication methods do in general exist (e.g. sshd_config may just be emtpy)
ssh -v server and look for the first "Authentications that can continue" line.
There is better way from here + modified by me for localhost case:
ssh -o PreferredAuthentications=none -o NoHostAuthenticationForLocalhost=yes localhost
nmap can do this too using ssh-auth-methods:
nmap -p 22 --script ssh-auth-methods localhost
Example output:
Starting Nmap 7.91 ( https://nmap.org ) at 2021-08-16 12:07 +07
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000087s latency).
PORT STATE SERVICE
22/tcp open ssh
| ssh-auth-methods:
| Supported authentication methods:
| publickey
|_ password
Nmap done: 1 IP address (1 host up) scanned in 0.26 seconds
What it does behind the scenes is in ssh-auth-methods.nse. Uses libssh2 to connect with a random username and lists out the possible authentication methods.
(It's possible to print out the effective sshd configuration options with sshd -T, this will show what options are in effect even if sshd_config is empty. For this use case running sshd -T | egrep 'permitrootlogin|authentication' would be useful.)
