diff --git a/examples/gmail_oauth2.rs b/examples/gmail_oauth2.rs
index 051c7e2..50805f1 100644
--- a/examples/gmail_oauth2.rs
+++ b/examples/gmail_oauth2.rs
@@ -2,7 +2,6 @@ extern crate base64;
 extern crate imap;
 extern crate native_tls;
 
-use base64::encode;
 use imap::authenticator::Authenticator;
 use native_tls::TlsConnector;
 
@@ -12,13 +11,12 @@ struct GmailOAuth2 {
 }
 
 impl Authenticator for GmailOAuth2 {
+    type Response = String;
     #[allow(unused_variables)]
-    fn process(&self, data: String) -> String {
-        encode(
-            format!(
-                "user={}\x01auth=Bearer {}\x01\x01",
-                self.user, self.access_token
-            ).as_bytes(),
+    fn process(&self, data: String) -> Self::Response {
+        format!(
+            "user={}\x01auth=Bearer {}\x01\x01",
+            self.user, self.access_token
         )
     }
 }
diff --git a/src/authenticator.rs b/src/authenticator.rs
index 825ec9a..0926924 100644
--- a/src/authenticator.rs
+++ b/src/authenticator.rs
@@ -1,4 +1,5 @@
 /// This will allow plugable authentication mechanisms.
 pub trait Authenticator {
-    fn process(&self, String) -> String;
+    type Response: AsRef<[u8]>;
+    fn process(&self, String) -> Self::Response;
 }
diff --git a/src/client.rs b/src/client.rs
index 8c1faf0..734d0e9 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -395,8 +395,8 @@ impl<T: Read + Write> Client<T> {
                     parse_authenticate_response(String::from_utf8(line).unwrap()),
                     self
                 );
-                let auth_response = base64::encode(authenticator.process(data).as_str());
-
+                let raw_response = &authenticator.process(data);
+                let auth_response = base64::encode(raw_response);
                 ok_or_unauth_client_err!(
                     self.write_line(auth_response.into_bytes().as_slice()),
                     self
@@ -948,8 +948,9 @@ mod tests {
         let client = Client::new(mock_stream);
         enum Authenticate { Auth };
         impl Authenticator for Authenticate {
-            fn process(&self, _: String) -> String {
-                "foo".to_string()
+            type Response = Vec<u8>;
+            fn process(&self, _: String) -> Self::Response {
+                b"foo".to_vec()
             }
         }
         let auth = Authenticate::Auth;