The ATEN/Supermicro KVM does not do standard VNC. Their protocol is a hacked up version of vnc’s RFB v3.8. It only supports a proprietary authentication protocol which it claims is type 16 (tight). Alas it is lying and it is not.
http://blog.flameeyes.eu/2012/07/more-on-the-supermicro-ikvm: The problem with the authentication is that for whatever the reason, it’s not a clear user/password auth. Instead it uses some hash or unique identifier, which changes each time I connect to the web interface — I’m not sure if it’s a hash, it’s definitely not an OTP (as I can start multiple instances of the javaws applet without having to re-download the JNLP), or just a nonce-based authentication, but it’s used both as user and as password. Actually I had a hunch while looking into it and I confirmed that what it uses is the same SID saved as a cookie after my login on the web interface.