Getting available authentication methods, and listing allowed methods

I may be wrong about this, but it seems that SSHClient._auth() always tries the same static set of authentication methods. This prevents the client from opting to use no authentication by passing 'none' as its only preferred authentication method. This is explicitly listed by the relevant RFC as being offered primarily to allow the client to see which authentication methods are available from the server.

For what it's worth, I was toying around with the paramiko auth options for a while, and found this SSH protocol feature on StackOverflow.

Beyond allowing the client more control over authentication, the 'none' option is useful for things like automated security scanning. It would be simple to write a function specifically for this purpose - something like SSHClient.supported_auth_methods(). If SSHClient._auth() were changed to allow user-specified authentication preferences, this function would just be a wrapper of SSHClient._auth() called with preferred_auth=['none'], or something like that.

Thanks for reading this, and thanks for writing this great package!
plsql

Start by reading SSHClient._auth() and the authentication-method behavior described in RFC 4252. Check how preferred methods are currently selected, then define how a supported_auth_methods-style entry point should report methods when 'none' is requested. Done means the client can request only the specified preference and expose the server's available authentication methods.