why openssh tries `none` authentication method

[Damien Miller]

Logu wrote:
> Hi,
> 
> I would like to know the significance of trying `none` method during 
> authentication sequence. Is there any way to avoid unnecessary trying of 
> this none authentication method first. 

The relevant section from draft-ietf-secsh-userauth explains this:

>    Authentication methods are identified by their name, as defined in
>    [SSH-ARCH].  The "none" method is reserved, and MUST NOT be listed as
>    supported.  However, it MAY be sent by the client.  The server MUST
>    always reject this request, unless the client is to be allowed in
>    without any authentication, in which case the server MUST accept this
>    request.  The main purpose of sending this request is to get the list
>    of supported methods from the server.