Disable username switching between SSH2 auth attempts, and add a

configurable option so users can re-enable the feature _if_ they
know they have an SSH2 server that isn't going to get shirty about
it. Inspired by a spectacular increase in OpenSSH's shirtiness.

[originally from svn r1474]

doc/config.but

@@ -1,4 +1,4 @@
-\versionid $Id: config.but,v 1.18 2001/12/06 20:05:39 simon Exp $
+\versionid $Id: config.but,v 1.19 2001/12/11 21:00:01 simon Exp $
 
 \C{config} Configuring PuTTY
 
@@ -1479,6 +1479,28 @@ See \k{pageant} for general information on Pageant, and
 there is a security risk involved with enabling this option; see
 \k{pageant-security} for details.
 
+\S{config-ssh-agentfwd} \q{Allow attempted changes of username in SSH2}
+
+\cfg{winhelp-topic}{ssh.auth.changeuser}
+
+In the SSH 1 protocol, it is impossible to change username after
+failing to authenticate. So if you mis-type your username at the
+PuTTY \q{login as:} prompt, you will not be able to change it except
+by restarting PuTTY.
+
+The SSH 2 protocol \e{does} allow changes of username, in principle,
+but does not make it mandatory for SSH 2 servers to accept them. In
+particular, OpenSSH does not accept a change of username; once you
+have sent one username, it will reject attempts to try to
+authenticate as another user. (Depending on the version of OpenSSH,
+it may quietly return failure for all login attempts, or it may send
+an error message.)
+
+For this reason, PuTTY will by default not prompt you for your
+username more than once, in case the server complains. If you know
+your server can cope with it, you can enable the \q{Allow attempted
+changes of username} option to modify PuTTY's behaviour.
+
 \S{config-ssh-privkey} \q{Private key file for authentication}
 
 \cfg{winhelp-topic}{ssh.auth.privkey}