Protocol / client plugin changes to support interactively asking for a PIN

remoting/protocol/negotiating_authenticator.h

 // Copyright (c) 2012 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_NEGOTIATING_AUTHENTICATOR_H_
 #define REMOTING_PROTOCOL_NEGOTIATING_AUTHENTICATOR_H_
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
 #include "remoting/protocol/authenticator.h"
 #include "remoting/protocol/authentication_method.h"
 
 namespace remoting {
 
 class RsaKeyPair;
 
 namespace protocol {
 
+typedef base::Callback<void(const std::string& secret)> SecretFetchedCallback;
+typedef base::Callback<void(
+    const SecretFetchedCallback& secret_fetched_callback)> FetchSecretCallback;
+
+// This class provides a meta-authenticator that allows clients and hosts that
+// support multiple authentication methods to negotiate a method to use.
+//
+// The typical flow is:
+//  * Client sends a message to host with its supported methods.
+//      (clients may additionally pick a method and send its first message).
+//  * Host picks a method and sends its first message (if any).
+//      (if a message for that method was sent by the client, it is processed).
+//  * Client creates the authenticator selected by the host. If the method
+//      starts with a message from the host, it is processed.
+//  * Client and host exchange messages until the authentication is ACCEPTED or
+//      REJECTED.
+//
+// The details:
+//  * CreateAuthenticator() may be asynchronous (i.e. require user interaction
+//      to determine initial parameters, like PIN). This happens inside
+//      ProcessMessage, so to the outside this behaves like any asynchronous
+//      message processing. Internally, CreateAuthenticator() receives a
+//      callback, that will resume the authentication once the authenticator is
+//      created. If there is already a message to be processed by the new
+//      authenticator, this callback includes a call to the underlying
+//      ProcessMessage().
+//  * Some authentication methods may have a specific starting direction (e.g.
+//      host always sends the first message), while others are versatile (e.g.
+//      SPAKE, where either side can send the first message). When an
+//      authenticator is created, it is given a preferred initial state, which
+//      the authenticator may ignore.
+//  * If the new authenticator state doesn't match the preferred one,
+//      the NegotiatingAuthenticator deals with that, by sending an empty
+//      <authenticator> stanza if the method has no message to send, and
+//      ignoring such empty messages on the receiving end.
+//  * The client may optimistically pick a method on its first message (assuming
+//      it doesn't require user interaction to start). If the host doesn't
+//      support that method, it will just discard that message, and choose
+//      another method from the client's supported methods list.
+//  * The host never sends its own supported methods back to the client, so once
+//      the host picks a method from the client's list, it's final.
+//  * Any change in this class must maintain compatibility between any version
+//      mix of webapp, client plugin and host, for both Me2Me and IT2Me.
 class NegotiatingAuthenticator : public Authenticator {
  public:
   virtual ~NegotiatingAuthenticator();
 
-  static bool IsNegotiableMessage(const buzz::XmlElement* message);
-
   // Creates a client authenticator for the given methods.
   static scoped_ptr<Authenticator> CreateForClient(
       const std::string& authentication_tag,
-      const std::string& shared_secret,
+      const FetchSecretCallback& fetch_secret_callback,
       const std::vector<AuthenticationMethod>& methods);
 
   // Creates a host authenticator, using a fixed shared secret/PIN hash.
   static scoped_ptr<Authenticator> CreateForHost(
       const std::string& local_cert,
       scoped_refptr<RsaKeyPair> key_pair,
       const std::string& shared_secret_hash,
       AuthenticationMethod::HashFunction hash_function);
 
   // 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:
-  NegotiatingAuthenticator(Authenticator::State initial_state);
+  explicit NegotiatingAuthenticator(Authenticator::State initial_state);
 
   void AddMethod(const AuthenticationMethod& method);
-  void CreateAuthenticator(State initial_state);
+
+  // (Asynchronously) creates an authenticator, and stores it in
+  // |current_authenticator_|. Authenticators that can be started in either
+  // state will be created in |preferred_initial_state|.
+  // |resume_callback| is called after |current_authenticator_| is set.
+  void CreateAuthenticator(Authenticator::State preferred_initial_state,
+                           const base::Closure& resume_callback);
+
+  // Calls |current_authenticator_| to process |message|, passing the supplied
+  // |resume_callback|.
+  void ProcessMessageInternal(const buzz::XmlElement* message,
+                              const base::Closure& resume_callback);
+
+  // Updates |state_| to reflect the current underlying authenticator state.
+  // |resume_callback| is called after the state is updated.
   void UpdateState(const base::Closure& resume_callback);
 
+  // Creates a V2Authenticator in state |initial_state| with the given
+  // |shared_secret|, then runs |resume_callback|.
+  void CreateV2AuthenticatorWithSecret(
+      Authenticator::State initial_state,
+      const base::Closure& resume_callback,
+      const std::string& shared_secret);
+
   bool is_host_side() const;
 
   // Used only for host authenticators.
   std::string local_cert_;
   scoped_refptr<RsaKeyPair> local_key_pair_;
   std::string shared_secret_hash_;
 
   // Used only for client authenticators.
   std::string authentication_tag_;
-  std::string shared_secret_;
+  FetchSecretCallback fetch_secret_callback_;
 
   // Used for both host and client authenticators.
   std::vector<AuthenticationMethod> methods_;
   AuthenticationMethod current_method_;
   scoped_ptr<Authenticator> current_authenticator_;
   State state_;
   RejectionReason rejection_reason_;
 
+  base::WeakPtrFactory<NegotiatingAuthenticator> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(NegotiatingAuthenticator);
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_NEGOTIATING_AUTHENTICATOR_H_