Error: com.jcraft.jsch.JSchException: Auth fail

[ianbale]

I've setup an SFTP server. It appears to work fine from most clients. I can connect, list files, change directories, upload / download files. create / delete directories, delete files etc.

However, one client (A "slightly modified" Jsch) fails to connect every time and results in an unhandled exception (listed below) that takes the server down.

Any idea why it might be doing this - and how to fix it?

Error: com.jcraft.jsch.JSchException: Auth fail
    at onDISCONNECT (/home/frog/noderail-data-feed-manager/node_modules/ssh2/node_modules/ssh2-streams/lib/ssh.js:2029:15)
    at SSH2Stream.<anonymous> (/home/frog/noderail-data-feed-manager/node_modules/ssh2/node_modules/ssh2-streams/lib/ssh.js:178:5)
    at emitMany (events.js:146:13)
    at SSH2Stream.emit (events.js:223:7)
    at parsePacket (/home/frog/noderail-data-feed-manager/node_modules/ssh2/node_modules/ssh2-streams/lib/ssh.js:3462:10)
    at SSH2Stream._transform (/home/frog/noderail-data-feed-manager/node_modules/ssh2/node_modules/ssh2-streams/lib/ssh.js:551:13)
    at SSH2Stream.Transform._read (_stream_transform.js:186:10)
    at SSH2Stream._read (/home/frog/noderail-data-feed-manager/node_modules/ssh2/node_modules/ssh2-streams/lib/ssh.js:212:15)
    at SSH2Stream.Transform._write (_stream_transform.js:174:12)
    at doWrite (_stream_writable.js:371:12)
    at writeOrBuffer (_stream_writable.js:357:5)
    at SSH2Stream.Writable.write (_stream_writable.js:274:11)
    at Socket.ondata (_stream_readable.js:628:20)
    at emitOne (events.js:115:13)
    at Socket.emit (events.js:210:7)
    at addChunk (_stream_readable.js:252:12) code: 3 }

With debugging on, I see only these two lines before the crash:

SFTP Server: on('authentication')
SFTP Server: error

It looks like the key exchange works okay, however as soon as the username is being send as part of the authentication the server sends back command 51 which is SSH_MSG_USERAUTH_FAILURE.

Strangely this is even before the password is being sent...