initial work towards server-side support

sasl/src/server/mechanisms/plain.rs

@@ -0,0 +1,13 @@
+use server::Mechanism;
+use common::{Secret, Credentials, Password};
+
+pub struct Plain {
+    password: String,
+}
+
+impl<V: Validator> Mechanism<V> for Plain {
+    fn name(&self) -> &str { "PLAIN" }
+
+    fn from_initial_message(validator: &V, msg: &[u8]) -> Result<(Self, String), String> {
+    }
+}