Unset a global preference.
.TP
.B user \fIUSER\fR \fIRESPONSE\fR
-Authenticate as \fIUSER\fR.
-.IP
-When a connection is made the server sends a \fB221\fR response before any
-command is received. This contains an algorithm name and a challenge encoded
-in hex. Currently the algorithm name is omitted if it is "sha1".
-.IP
-The \fIRESPONSE\fR consists of the selected hash of the user's password
-concatenated with the challenge, encoded in hex.
+Authenticate as \fIUSER\fR. See
+.B AUTHENTICATION
+below.
.TP
.B version
Send back a response with the server version as the second field.
The text part is just commentary (but would normally be a response for this
command) e.g. \fBplaying\fR.
.SH AUTHENTICATION
-The server starts by issuing a challenge line, with response code 231. This
-contains a random challenge encoded in hex.
+When a connection is made the server sends a \fB231\fR response before any
+command is received. This contains an algorithm name and a challenge encoded
+in hex.
+.PP
+Currently the algorithm name is omitted if it is \fBsha1\fR (but this will
+probably change in a future version). The other options are \fBsha256\fR,
+\fBsha384\fR and \fBsha512\fR. \fBSHA1\fR etc work as synonyms.
.PP
-The client should send back a \fBuser\fR command with username and a
-hex-encoded response. The response is the SHA-1 hash of the user's password
-and the challenge.
+The \fBuser\fR response consists of the selected hash of the user's password
+concatenated with the challenge, encoded in hex.
.SH "TRACK INFORMATION"
Track information is encoded in a line (i.e. using the usual line syntax) as
pairs of fields. The first is a name, the second a value. The names have the