PairingAuthenticator implementation and plumbing.

remoting/protocol/pairing_client_authenticator.h

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_PROTOCOL_PAIRING_CLIENT_AUTHENTICATOR_H_
+#define REMOTING_PROTOCOL_PAIRING_CLIENT_AUTHENTICATOR_H_
+
+#include "base/memory/weak_ptr.h"
+#include "remoting/protocol/authenticator.h"
+
+namespace remoting {
+
+class RsaKeyPair;
+
+namespace protocol {
+
+class Authenticator;
+
+typedef base::Callback<void(const std::string& secret)> SecretFetchedCallback;
+typedef base::Callback<void(
+    const SecretFetchedCallback& secret_fetched_callback)> FetchSecretCallback;
+
+// PairingClientAuthenticator builds on top of V2Authenticator to add
+// support for PIN-less authentication via device pairing:
+//
+// * If a client device is already paired, it includes a client id in
+//   the initial authentication message.
+// * If the host recognizes the id, it looks up the corresponding
+//   shared secret and the rest of the protocol is host-initiated
+//   SPAKE with HMAC_SHA256.
+// * If it does not recognize the id, it sends an error message to
+//   the client, which will prompt the user for a PIN to use for
+//   authentication instead. In this case, the rest of the procotol
+//   is client-initiated SPAKE with HMAC_SHA256.
+//
+// If a client device is not already paired, but supports pairing, it
+// sends an empty initial authentication message. In this case, the
+// authenticator behaves exactly like the V2Authenticator with
+// HMAC_SHA256--only the protocol type differs, which the client uses

[rmsousa, 2013/05/16 00:46:25]

nit: s/protocol type/method name/

[Jamie, 2013/05/16 19:30:16]

Done.

+// to detect that pairing should be offered to the user.
+class PairingClientAuthenticator : public Authenticator {
+ public:
+  PairingClientAuthenticator(
+      const std::string& client_id,
+      const std::string& shared_secret,
+      const FetchSecretCallback& fetch_secret_callback,
+      const std::string& authentication_tag);
+  virtual ~PairingClientAuthenticator() {}
+
+  // Authenticator interface.
+  virtual State state() const OVERRIDE;
+  virtual RejectionReason rejection_reason() const OVERRIDE;
+  virtual void ProcessMessage(const buzz::XmlElement* message,
+                              const base::Closure& resume_callback) OVERRIDE;
+  virtual scoped_ptr<buzz::XmlElement> GetNextMessage() OVERRIDE;
+  virtual scoped_ptr<ChannelAuthenticator>
+      CreateChannelAuthenticator() const OVERRIDE;
+
+ private:
+  void CreateV2AuthenticatorWithSecret(const base::Closure& resume_callback,
+                                       const std::string& secret);
+
+  // |pairing_state_| indicates the progress of the initial pairing client
+  // id exchange. MESSAGE_READY, WAITING_MESSAGE and PROCESSING_MESSAGE map
+  // directly to the corresponding return value from the |state| method (the
+  // latter means that the user is being prompted for the PIN). ACCEPTED and
+  // REJECTED mean that the client id exchange is complete and succeeded or
+  // failed, respectively. Currently, no distinction is made between these
+  // two states--in either case the underlying v2 authenticator has been
+  // created and holds the state of the overall auth exchange.
+  State pairing_state_;
+
+  std::string client_id_;
+  const std::string& shared_secret_;
+  FetchSecretCallback fetch_secret_callback_;
+  std::string authentication_tag_;
+  State initial_state_;
+  scoped_ptr<Authenticator> v2_authenticator_;
+  bool pairing_failed_;
+  base::WeakPtrFactory<PairingClientAuthenticator> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(PairingClientAuthenticator);
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_H_