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Fixes #113

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>

vendor/github.com/godbus/dbus/auth_external.go

@@ -0,0 +1,26 @@
+package dbus
+
+import (
+	"encoding/hex"
+)
+
+// AuthExternal returns an Auth that authenticates as the given user with the
+// EXTERNAL mechanism.
+func AuthExternal(user string) Auth {
+	return authExternal{user}
+}
+
+// AuthExternal implements the EXTERNAL authentication mechanism.
+type authExternal struct {
+	user string
+}
+
+func (a authExternal) FirstData() ([]byte, []byte, AuthStatus) {
+	b := make([]byte, 2*len(a.user))
+	hex.Encode(b, []byte(a.user))
+	return []byte("EXTERNAL"), b, AuthOk
+}
+
+func (a authExternal) HandleData(b []byte) ([]byte, AuthStatus) {
+	return nil, AuthError
+}