initial work towards server-side support

sasl/src/client/mechanisms/plain.rs

@@ -0,0 +1,50 @@
+//! Provides the SASL "PLAIN" mechanism.
+
+use client::Mechanism;
+use common::{Credentials, Identity, Password, Secret};
+
+/// A struct for the SASL PLAIN mechanism.
+pub struct Plain {
+    username: String,
+    password: String,
+}
+
+impl Plain {
+    /// Constructs a new struct for authenticating using the SASL PLAIN mechanism.
+    ///
+    /// It is recommended that instead you use a `Credentials` struct and turn it into the
+    /// requested mechanism using `from_credentials`.
+    pub fn new<N: Into<String>, P: Into<String>>(username: N, password: P) -> Plain {
+        Plain {
+            username: username.into(),
+            password: password.into(),
+        }
+    }
+}
+
+impl Mechanism for Plain {
+    fn name(&self) -> &str {
+        "PLAIN"
+    }
+
+    fn from_credentials(credentials: Credentials) -> Result<Plain, String> {
+        if let Secret::Password(Password::Plain(password)) = credentials.secret {
+            if let Identity::Username(username) = credentials.identity {
+                Ok(Plain::new(username, password))
+            } else {
+                Err("PLAIN requires a username".to_owned())
+            }
+        } else {
+            Err("PLAIN requires a plaintext password".to_owned())
+        }
+    }
+
+    fn initial(&mut self) -> Result<Vec<u8>, String> {
+        let mut auth = Vec::new();
+        auth.push(0);
+        auth.extend(self.username.bytes());
+        auth.push(0);
+        auth.extend(self.password.bytes());
+        Ok(auth)
+    }
+}