diff --git a/nix-dist/build+upload.sh b/nix-dist/build+upload.sh
index c925eeaef3d5..7cae11658c87 100755
--- a/nix-dist/build+upload.sh
+++ b/nix-dist/build+upload.sh
@@ -2,7 +2,13 @@
 
 url="https://svn.cs.uu.nl:12443/repos/trace/nix/trunk/"
 
-curl="curl -f --silent -S"
+curl="curl --fail --silent --show-error"
+# auth-info file should have format `username:password'.
+if ! auth_info=$(cat auth-info); then
+    echo "cannot get authentication info"
+    exit 1
+fi
+curl_up="$curl --user $auth_info"
 
 rev=$(svn log --quiet --non-interactive "$url" \
     | grep '^r' \
@@ -15,9 +21,10 @@ fi
 
 echo "building revision $rev of $url"
 
+# !!! race
 echo $rev > head-revision.nix
 
-if ! storeexprs=($(nix-instantiate -vvv do-it.nix)); then exit 1; fi
+if ! storeexprs=($(nix-instantiate -vv do-it.nix)); then exit 1; fi
 
 srcexpr=${storeexprs[0]}
 testexpr=${storeexprs[1]}
@@ -32,36 +39,40 @@ relname=$((cd $outpath && echo nix-*.tar.bz2) | sed -e s/.tar.bz2//)
 echo "release is $relname"
 
 # If it already exists on the server, quit.
-exists=$($curl $uploader/exists/$relname)
+if ! exists=$($curl_up $uploader/exists/$relname); then
+    echo "cannot check for existence of $relname on the server"
+    exit 1
+fi
 if test "$exists" = "yes"; then
     echo "server already has release $relname"
     exit 0
 fi
 
 # Create an upload session on the server.
-if ! sessionname=$($curl $uploader/create/$relname); then
+if ! sessionname=$($curl_up $uploader/create/$relname); then
     echo "cannot create upload session"
     exit 1
 fi
 echo "session name is $sessionname"
 
 # Upload the source distribution and the manual.
-$curl -T "$outpath"/nix-*.tar.bz2 "$uploader/upload/$sessionname/" || exit 1
-$curl -T "$outpath"/manual.tar.bz2 "$uploader/upload-tar/$sessionname" || exit 1
+$curl_up -T "$outpath"/nix-*.tar.bz2 "$uploader/upload/$sessionname/" || exit 1
+$curl_up -T "$outpath"/manual.tar.bz2 "$uploader/upload-tar/$sessionname" || exit 1
 
 # Perform a test build.
 #if ! nix-store -vvvv -r "$testexpr" > /dev/null; then exit 1; fi
 
 # Perform an RPM build, and upload the RPM to the server.
 if ! rpmpath=$(nix-store -vvvv -qnf "$rpmexpr"); then exit 1; fi
-$curl -T "$rpmpath"/nix-*.rpm "$uploader/upload/$sessionname/" || exit 1
+$curl_up -T "$rpmpath"/nix-*.rpm "$uploader/upload/$sessionname/" || exit 1
 
 # Finish the upload session.
-$curl "$uploader/finish/$sessionname" || exit 1
+$curl_up "$uploader/finish/$sessionname" || exit 1
 
 # Publish the release on the Wiki.
+# !!! create /tmp file
 echo -n $relname > relname
-$curl -T relname "$uploader/put/head-revision" || exit 1
+$curl_up -T relname "$uploader/put/head-revision" || exit 1
 rm -f $relname
 
 # Force a refresh of the Wiki.