google_apis/gaia/oauth2_access_token_manager.cc

// Copyright 2019 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.

#include "google_apis/gaia/oauth2_access_token_manager.h"

#include "base/metrics/histogram_macros.h"
#include "base/rand_util.h"
#include "base/threading/thread_task_runner_handle.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
#include "google_apis/gaia/gaia_urls.h"
#include "google_apis/gaia/oauth2_access_token_fetcher.h"
#include "services/network/public/cpp/shared_url_loader_factory.h"

int OAuth2AccessTokenManager::max_fetch_retry_num_ = 5;

OAuth2AccessTokenManager::Delegate::Delegate() = default;

OAuth2AccessTokenManager::Delegate::~Delegate() = default;

bool OAuth2AccessTokenManager::Delegate::FixRequestErrorIfPossible() {
  return false;
}

scoped_refptr<network::SharedURLLoaderFactory>
OAuth2AccessTokenManager::Delegate::GetURLLoaderFactory() const {
  return nullptr;
}

bool OAuth2AccessTokenManager::Delegate::HandleAccessTokenFetch(
    RequestImpl* request,
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes) {
  return false;
}

OAuth2AccessTokenManager::Request::Request() {}

OAuth2AccessTokenManager::Request::~Request() {}

OAuth2AccessTokenManager::Consumer::Consumer(const std::string& id) : id_(id) {}

OAuth2AccessTokenManager::Consumer::~Consumer() {}

OAuth2AccessTokenManager::RequestImpl::RequestImpl(
    const CoreAccountId& account_id,
    Consumer* consumer)
    : account_id_(account_id), consumer_(consumer) {}

OAuth2AccessTokenManager::RequestImpl::~RequestImpl() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
}

CoreAccountId OAuth2AccessTokenManager::RequestImpl::GetAccountId() const {
  return account_id_;
}

std::string OAuth2AccessTokenManager::RequestImpl::GetConsumerId() const {
  return consumer_->id();
}

void OAuth2AccessTokenManager::RequestImpl::InformConsumer(
    const GoogleServiceAuthError& error,
    const OAuth2AccessTokenConsumer::TokenResponse& token_response) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (error.state() == GoogleServiceAuthError::NONE)
    consumer_->OnGetTokenSuccess(this, token_response);
  else
    consumer_->OnGetTokenFailure(this, error);
}

OAuth2AccessTokenManager::RequestParameters::RequestParameters(
    const std::string& client_id,
    const CoreAccountId& account_id,
    const ScopeSet& scopes)
    : client_id(client_id), account_id(account_id), scopes(scopes) {}

OAuth2AccessTokenManager::RequestParameters::RequestParameters(
    const RequestParameters& other) = default;

OAuth2AccessTokenManager::RequestParameters::~RequestParameters() {}

bool OAuth2AccessTokenManager::RequestParameters::operator<(
    const RequestParameters& p) const {
  if (client_id < p.client_id)
    return true;
  else if (p.client_id < client_id)
    return false;

  if (account_id < p.account_id)
    return true;
  else if (p.account_id < account_id)
    return false;

  return scopes < p.scopes;
}

// Class that fetches an OAuth2 access token for a given account id and set of
// scopes.
//
// It aims to meet OAuth2AccessTokenManager's requirements on token fetching.
// Retry mechanism is used to handle failures.
//
// To use this class, call CreateAndStart() to create and start a Fetcher.
//
// The Fetcher will call back the token manager by calling
// OAuth2AccessTokenManager::OnFetchComplete() when it completes fetching, if
// it is not destroyed before it completes fetching; if the Fetcher is destroyed
// before it completes fetching, the token manager will never be called back.
// The Fetcher destroys itself after calling back the manager when it finishes
// fetching.
//
// Requests that are waiting for the fetching results of this Fetcher can be
// added to the Fetcher by calling
// OAuth2AccessTokenManager::Fetcher::AddWaitingRequest() before the Fetcher
// completes fetching.
//
// The waiting requests are taken as weak pointers and they can be deleted.
// They will be called back with the result when either the Fetcher completes
// fetching or is destroyed, whichever comes first. In the latter case, the
// waiting requests will be called back with an error.
//
// The OAuth2AccessTokenManager and the waiting requests will never be called
// back on the same turn of the message loop as when the fetcher is started,
// even if an immediate error occurred.
class OAuth2AccessTokenManager::Fetcher : public OAuth2AccessTokenConsumer {
 public:
  // Creates a Fetcher and starts fetching an OAuth2 access token for
  // |account_id| and |scopes| in the request context obtained by |getter|.
  // The given |oauth2_access_token_manager| will be informed when fetching is
  // done.
  static std::unique_ptr<OAuth2AccessTokenManager::Fetcher> CreateAndStart(
      OAuth2AccessTokenManager* oauth2_access_token_manager,
      const CoreAccountId& account_id,
      scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
      const std::string& client_id,
      const std::string& client_secret,
      const ScopeSet& scopes,
      base::WeakPtr<RequestImpl> waiting_request);
  ~Fetcher() override;

  // Add a request that is waiting for the result of this Fetcher.
  void AddWaitingRequest(base::WeakPtr<RequestImpl> waiting_request);

  // Returns count of waiting requests.
  size_t GetWaitingRequestCount() const;

  const std::vector<base::WeakPtr<RequestImpl>>& waiting_requests() const {
    return waiting_requests_;
  }

  void Cancel();

  const ScopeSet& GetScopeSet() const;
  const std::string& GetClientId() const;
  const CoreAccountId& GetAccountId() const;

  // The error result from this fetcher.
  const GoogleServiceAuthError& error() const { return error_; }

 protected:
  // OAuth2AccessTokenConsumer
  void OnGetTokenSuccess(
      const OAuth2AccessTokenConsumer::TokenResponse& token_response) override;
  void OnGetTokenFailure(const GoogleServiceAuthError& error) override;

 private:
  Fetcher(OAuth2AccessTokenManager* oauth2_access_token_manager,
          const CoreAccountId& account_id,
          scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
          const std::string& client_id,
          const std::string& client_secret,
          const ScopeSet& scopes,
          base::WeakPtr<RequestImpl> waiting_request);
  void Start();
  void InformWaitingRequests();
  void InformWaitingRequestsAndDelete();
  bool ShouldRetry(const GoogleServiceAuthError& error) const;
  int64_t ComputeExponentialBackOffMilliseconds(int retry_num);

  // Attempts to retry the fetch if possible.  This is possible if the retry
  // count has not been exceeded.  Returns true if a retry has been restarted
  // and false otherwise.
  bool RetryIfPossible(const GoogleServiceAuthError& error);

  // |oauth2_access_token_manager_| remains valid for the life of this
  // Fetcher, since this Fetcher is destructed in the dtor of the
  // OAuth2AccessTokenManager or is scheduled for deletion at the end of
  // OnGetTokenFailure/OnGetTokenSuccess (whichever comes first).
  OAuth2AccessTokenManager* const oauth2_access_token_manager_;
  scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory_;
  const CoreAccountId account_id_;
  const ScopeSet scopes_;
  std::vector<base::WeakPtr<RequestImpl>> waiting_requests_;

  int retry_number_;
  base::OneShotTimer retry_timer_;
  std::unique_ptr<OAuth2AccessTokenFetcher> fetcher_;

  // Variables that store fetch results.
  // Initialized to be GoogleServiceAuthError::SERVICE_UNAVAILABLE to handle
  // destruction.
  GoogleServiceAuthError error_;
  OAuth2AccessTokenConsumer::TokenResponse token_response_;

  // OAuth2 client id and secret.
  std::string client_id_;
  std::string client_secret_;

  DISALLOW_COPY_AND_ASSIGN(Fetcher);
};

// static
std::unique_ptr<OAuth2AccessTokenManager::Fetcher>
OAuth2AccessTokenManager::Fetcher::CreateAndStart(
    OAuth2AccessTokenManager* oauth2_access_token_manager,
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes,
    base::WeakPtr<RequestImpl> waiting_request) {
  std::unique_ptr<OAuth2AccessTokenManager::Fetcher> fetcher = base::WrapUnique(
      new Fetcher(oauth2_access_token_manager, account_id, url_loader_factory,
                  client_id, client_secret, scopes, waiting_request));

  fetcher->Start();
  return fetcher;
}

OAuth2AccessTokenManager::Fetcher::Fetcher(
    OAuth2AccessTokenManager* oauth2_access_token_manager,
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes,
    base::WeakPtr<RequestImpl> waiting_request)
    : oauth2_access_token_manager_(oauth2_access_token_manager),
      url_loader_factory_(url_loader_factory),
      account_id_(account_id),
      scopes_(scopes),
      retry_number_(0),
      error_(GoogleServiceAuthError::SERVICE_UNAVAILABLE),
      client_id_(client_id),
      client_secret_(client_secret) {
  DCHECK(oauth2_access_token_manager_);
  waiting_requests_.push_back(waiting_request);
}

OAuth2AccessTokenManager::Fetcher::~Fetcher() {
  // Inform the waiting requests if it has not done so.
  if (waiting_requests_.size())
    InformWaitingRequests();
}

void OAuth2AccessTokenManager::Fetcher::Start() {
  fetcher_ = oauth2_access_token_manager_->CreateAccessTokenFetcher(
      account_id_, url_loader_factory_, this);
  DCHECK(fetcher_);

  // Stop the timer before starting the fetch, as defense in depth against the
  // fetcher calling us back synchronously (which might restart the timer).
  retry_timer_.Stop();
  fetcher_->Start(client_id_, client_secret_,
                  std::vector<std::string>(scopes_.begin(), scopes_.end()));
}

void OAuth2AccessTokenManager::Fetcher::OnGetTokenSuccess(
    const OAuth2AccessTokenConsumer::TokenResponse& token_response) {
  fetcher_.reset();

  // Fetch completes.
  error_ = GoogleServiceAuthError::AuthErrorNone();
  token_response_ = token_response;

  // Delegates may override this method to skip caching in some cases, but
  // we still inform all waiting Consumers of a successful token fetch below.
  // This is intentional -- some consumers may need the token for cleanup
  // tasks. https://chromiumcodereview.appspot.com/11312124/
  oauth2_access_token_manager_->RegisterTokenResponse(client_id_, account_id_,
                                                      scopes_, token_response_);
  InformWaitingRequestsAndDelete();
}

void OAuth2AccessTokenManager::Fetcher::OnGetTokenFailure(
    const GoogleServiceAuthError& error) {
  fetcher_.reset();

  if (ShouldRetry(error) && RetryIfPossible(error))
    return;

  UMA_HISTOGRAM_ENUMERATION("Signin.OAuth2TokenGetFailure", error.state(),
                            GoogleServiceAuthError::NUM_STATES);
  error_ = error;
  InformWaitingRequestsAndDelete();
}

// Returns an exponential backoff in milliseconds including randomness less than
// 1000 ms when retrying fetching an OAuth2 access token.
int64_t
OAuth2AccessTokenManager::Fetcher::ComputeExponentialBackOffMilliseconds(
    int retry_num) {
  DCHECK(retry_num < oauth2_access_token_manager_->max_fetch_retry_num_);
  int exponential_backoff_in_seconds = 1 << retry_num;
  // Returns a backoff with randomness < 1000ms
  return (exponential_backoff_in_seconds + base::RandDouble()) * 1000;
}

bool OAuth2AccessTokenManager::Fetcher::RetryIfPossible(
    const GoogleServiceAuthError& error) {
  if (retry_number_ < oauth2_access_token_manager_->max_fetch_retry_num_) {
    base::TimeDelta backoff = base::TimeDelta::FromMilliseconds(
        ComputeExponentialBackOffMilliseconds(retry_number_));
    ++retry_number_;
    UMA_HISTOGRAM_ENUMERATION("Signin.OAuth2TokenGetRetry", error.state(),
                              GoogleServiceAuthError::NUM_STATES);
    retry_timer_.Stop();
    retry_timer_.Start(FROM_HERE, backoff, this,
                       &OAuth2AccessTokenManager::Fetcher::Start);
    return true;
  }

  return false;
}

bool OAuth2AccessTokenManager::Fetcher::ShouldRetry(
    const GoogleServiceAuthError& error) const {
  GoogleServiceAuthError::State error_state = error.state();
  bool should_retry =
      error_state == GoogleServiceAuthError::CONNECTION_FAILED ||
      error_state == GoogleServiceAuthError::REQUEST_CANCELED ||
      error_state == GoogleServiceAuthError::SERVICE_UNAVAILABLE;

  // Give the delegate a chance to correct the error first.  This is a best
  // effort only.
  return should_retry || oauth2_access_token_manager_->GetDelegate()
                             ->FixRequestErrorIfPossible();
}

void OAuth2AccessTokenManager::Fetcher::InformWaitingRequests() {
  for (const base::WeakPtr<RequestImpl>& request : waiting_requests_) {
    if (request)
      request->InformConsumer(error_, token_response_);
  }
  waiting_requests_.clear();
}

void OAuth2AccessTokenManager::Fetcher::InformWaitingRequestsAndDelete() {
  // Deregisters itself from the manager to prevent more waiting requests to
  // be added when it calls back the waiting requests.
  oauth2_access_token_manager_->OnFetchComplete(this);
  InformWaitingRequests();
  base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, this);
}

void OAuth2AccessTokenManager::Fetcher::AddWaitingRequest(
    base::WeakPtr<RequestImpl> waiting_request) {
  waiting_requests_.push_back(waiting_request);
}

size_t OAuth2AccessTokenManager::Fetcher::GetWaitingRequestCount() const {
  return waiting_requests_.size();
}

void OAuth2AccessTokenManager::Fetcher::Cancel() {
  if (fetcher_)
    fetcher_->CancelRequest();
  fetcher_.reset();
  retry_timer_.Stop();
  error_ = GoogleServiceAuthError(GoogleServiceAuthError::REQUEST_CANCELED);
  InformWaitingRequestsAndDelete();
}

const OAuth2AccessTokenManager::ScopeSet&
OAuth2AccessTokenManager::Fetcher::GetScopeSet() const {
  return scopes_;
}

const std::string& OAuth2AccessTokenManager::Fetcher::GetClientId() const {
  return client_id_;
}

const CoreAccountId& OAuth2AccessTokenManager::Fetcher::GetAccountId() const {
  return account_id_;
}

OAuth2AccessTokenManager::OAuth2AccessTokenManager(
    OAuth2AccessTokenManager::Delegate* delegate)
    : delegate_(delegate) {
  DCHECK(delegate_);
}

OAuth2AccessTokenManager::~OAuth2AccessTokenManager() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // Release all the pending fetchers.
  pending_fetchers_.clear();
}

OAuth2AccessTokenManager::Delegate* OAuth2AccessTokenManager::GetDelegate() {
  return delegate_;
}

const OAuth2AccessTokenManager::Delegate*
OAuth2AccessTokenManager::GetDelegate() const {
  return delegate_;
}

void OAuth2AccessTokenManager::AddDiagnosticsObserver(
    DiagnosticsObserver* observer) {
  diagnostics_observer_list_.AddObserver(observer);
}

void OAuth2AccessTokenManager::RemoveDiagnosticsObserver(
    DiagnosticsObserver* observer) {
  diagnostics_observer_list_.RemoveObserver(observer);
}

std::unique_ptr<OAuth2AccessTokenManager::Request>
OAuth2AccessTokenManager::StartRequest(const CoreAccountId& account_id,
                                       const ScopeSet& scopes,
                                       Consumer* consumer) {
  return StartRequestForClientWithContext(
      account_id, delegate_->GetURLLoaderFactory(),
      GaiaUrls::GetInstance()->oauth2_chrome_client_id(),
      GaiaUrls::GetInstance()->oauth2_chrome_client_secret(), scopes, consumer);
}

std::unique_ptr<OAuth2AccessTokenManager::Request>
OAuth2AccessTokenManager::StartRequestForClient(
    const CoreAccountId& account_id,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes,
    Consumer* consumer) {
  return StartRequestForClientWithContext(
      account_id, delegate_->GetURLLoaderFactory(), client_id, client_secret,
      scopes, consumer);
}

std::unique_ptr<OAuth2AccessTokenManager::Request>
OAuth2AccessTokenManager::StartRequestWithContext(
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const ScopeSet& scopes,
    Consumer* consumer) {
  return StartRequestForClientWithContext(
      account_id, url_loader_factory,
      GaiaUrls::GetInstance()->oauth2_chrome_client_id(),
      GaiaUrls::GetInstance()->oauth2_chrome_client_secret(), scopes, consumer);
}

void OAuth2AccessTokenManager::FetchOAuth2Token(
    RequestImpl* request,
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes) {
  // If there is already a pending fetcher for |scopes| and |account_id|,
  // simply register this |request| for those results rather than starting
  // a new fetcher.
  RequestParameters request_parameters =
      RequestParameters(client_id, account_id, scopes);
  auto iter = pending_fetchers_.find(request_parameters);
  if (iter != pending_fetchers_.end()) {
    iter->second->AddWaitingRequest(request->AsWeakPtr());
    return;
  }

  pending_fetchers_[request_parameters] =
      Fetcher::CreateAndStart(this, account_id, url_loader_factory, client_id,
                              client_secret, scopes, request->AsWeakPtr());
}

void OAuth2AccessTokenManager::RegisterTokenResponse(
    const std::string& client_id,
    const CoreAccountId& account_id,
    const ScopeSet& scopes,
    const OAuth2AccessTokenConsumer::TokenResponse& token_response) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  token_cache_[RequestParameters(client_id, account_id, scopes)] =
      token_response;
}

const OAuth2AccessTokenConsumer::TokenResponse*
OAuth2AccessTokenManager::GetCachedTokenResponse(
    const RequestParameters& request_parameters) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  TokenCache::iterator token_iterator = token_cache_.find(request_parameters);
  if (token_iterator == token_cache_.end())
    return nullptr;
  if (token_iterator->second.expiration_time <= base::Time::Now()) {
    token_cache_.erase(token_iterator);
    return nullptr;
  }
  return &token_iterator->second;
}

void OAuth2AccessTokenManager::ClearCache() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  for (const auto& entry : token_cache_) {
    for (auto& observer : diagnostics_observer_list_)
      observer.OnAccessTokenRemoved(entry.first.account_id, entry.first.scopes);
  }

  token_cache_.clear();
}

void OAuth2AccessTokenManager::ClearCacheForAccount(
    const CoreAccountId& account_id) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  for (TokenCache::iterator iter = token_cache_.begin();
       iter != token_cache_.end();
       /* iter incremented in body */) {
    if (iter->first.account_id == account_id) {
      for (auto& observer : diagnostics_observer_list_)
        observer.OnAccessTokenRemoved(account_id, iter->first.scopes);
      token_cache_.erase(iter++);
    } else {
      ++iter;
    }
  }
}

void OAuth2AccessTokenManager::CancelAllRequests() {
  std::vector<Fetcher*> fetchers_to_cancel;
  for (const auto& pending_fetcher : pending_fetchers_)
    fetchers_to_cancel.push_back(pending_fetcher.second.get());
  CancelFetchers(fetchers_to_cancel);
}

void OAuth2AccessTokenManager::CancelRequestsForAccount(
    const CoreAccountId& account_id) {
  std::vector<Fetcher*> fetchers_to_cancel;
  for (const auto& pending_fetcher : pending_fetchers_) {
    if (pending_fetcher.first.account_id == account_id)
      fetchers_to_cancel.push_back(pending_fetcher.second.get());
  }
  CancelFetchers(fetchers_to_cancel);
}

void OAuth2AccessTokenManager::InvalidateAccessToken(
    const CoreAccountId& account_id,
    const ScopeSet& scopes,
    const std::string& access_token) {
  InvalidateAccessTokenImpl(account_id,
                            GaiaUrls::GetInstance()->oauth2_chrome_client_id(),
                            scopes, access_token);
}

void OAuth2AccessTokenManager::InvalidateAccessTokenImpl(
    const CoreAccountId& account_id,
    const std::string& client_id,
    const ScopeSet& scopes,
    const std::string& access_token) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  RemoveCachedTokenResponse(RequestParameters(client_id, account_id, scopes),
                            access_token);
  delegate_->OnAccessTokenInvalidated(account_id, client_id, scopes,
                                      access_token);
}

void OAuth2AccessTokenManager::
    set_max_authorization_token_fetch_retries_for_testing(int max_retries) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  max_fetch_retry_num_ = max_retries;
}

size_t OAuth2AccessTokenManager::GetNumPendingRequestsForTesting(
    const std::string& client_id,
    const CoreAccountId& account_id,
    const ScopeSet& scopes) const {
  auto iter =
      pending_fetchers_.find(RequestParameters(client_id, account_id, scopes));
  return iter == pending_fetchers_.end()
             ? 0
             : iter->second->GetWaitingRequestCount();
}

const base::ObserverList<OAuth2AccessTokenManager::DiagnosticsObserver,
                         true>::Unchecked&
OAuth2AccessTokenManager::GetDiagnosticsObserversForTesting() {
  return diagnostics_observer_list_;
}

std::unique_ptr<OAuth2AccessTokenFetcher>
OAuth2AccessTokenManager::CreateAccessTokenFetcher(
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    OAuth2AccessTokenConsumer* consumer) {
  return delegate_->CreateAccessTokenFetcher(account_id, url_loader_factory,
                                             consumer);
}

std::unique_ptr<OAuth2AccessTokenManager::Request>
OAuth2AccessTokenManager::StartRequestForClientWithContext(
    const CoreAccountId& account_id,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    const std::string& client_id,
    const std::string& client_secret,
    const ScopeSet& scopes,
    Consumer* consumer) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  std::unique_ptr<RequestImpl> request(new RequestImpl(account_id, consumer));
  for (auto& observer : diagnostics_observer_list_)
    observer.OnAccessTokenRequested(account_id, consumer->id(), scopes);

  if (!delegate_->HasRefreshToken(account_id)) {
    GoogleServiceAuthError error(GoogleServiceAuthError::USER_NOT_SIGNED_UP);

    for (auto& observer : diagnostics_observer_list_) {
      observer.OnFetchAccessTokenComplete(account_id, consumer->id(), scopes,
                                          error, base::Time());
    }

    base::ThreadTaskRunnerHandle::Get()->PostTask(
        FROM_HERE,
        base::BindOnce(&RequestImpl::InformConsumer, request->AsWeakPtr(),
                       error, OAuth2AccessTokenConsumer::TokenResponse()));
    return std::move(request);
  }

  RequestParameters request_parameters(client_id, account_id, scopes);
  const OAuth2AccessTokenConsumer::TokenResponse* token_response =
      GetCachedTokenResponse(request_parameters);
  if (token_response && token_response->access_token.length()) {
    InformConsumerWithCachedTokenResponse(token_response, request.get(),
                                          request_parameters);
  } else if (delegate_->HandleAccessTokenFetch(request.get(), account_id,
                                               url_loader_factory, client_id,
                                               client_secret, scopes)) {
    // The delegate handling the fetch request means that we *don't* perform a
    // fetch.
  } else {
    // The token isn't in the cache and the delegate isn't fetching it: fetch it
    // ourselves!
    FetchOAuth2Token(request.get(), account_id, url_loader_factory, client_id,
                     client_secret, scopes);
  }
  return std::move(request);
}

void OAuth2AccessTokenManager::InformConsumerWithCachedTokenResponse(
    const OAuth2AccessTokenConsumer::TokenResponse* cache_token_response,
    RequestImpl* request,
    const RequestParameters& request_parameters) {
  DCHECK(cache_token_response && cache_token_response->access_token.length());
  for (auto& observer : diagnostics_observer_list_) {
    observer.OnFetchAccessTokenComplete(
        request_parameters.account_id, request->GetConsumerId(),
        request_parameters.scopes, GoogleServiceAuthError::AuthErrorNone(),
        cache_token_response->expiration_time);
  }
  base::ThreadTaskRunnerHandle::Get()->PostTask(
      FROM_HERE,
      base::BindOnce(&RequestImpl::InformConsumer, request->AsWeakPtr(),
                     GoogleServiceAuthError(GoogleServiceAuthError::NONE),
                     *cache_token_response));
}

bool OAuth2AccessTokenManager::RemoveCachedTokenResponse(
    const RequestParameters& request_parameters,
    const std::string& token_to_remove) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  TokenCache::iterator token_iterator = token_cache_.find(request_parameters);
  if (token_iterator != token_cache_.end() &&
      token_iterator->second.access_token == token_to_remove) {
    for (auto& observer : diagnostics_observer_list_) {
      observer.OnAccessTokenRemoved(request_parameters.account_id,
                                    request_parameters.scopes);
    }
    token_cache_.erase(token_iterator);
    return true;
  }
  return false;
}

void OAuth2AccessTokenManager::OnFetchComplete(
    OAuth2AccessTokenManager::Fetcher* fetcher) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  delegate_->OnAccessTokenFetched(fetcher->GetAccountId(), fetcher->error());

  // Note |fetcher| is recorded in |pending_fetcher_| mapped from its
  // combination of client ID, account ID, and scope set. This is guaranteed as
  // follows; here a Fetcher is said to be uncompleted if it has not finished
  // calling back
  // OAuth2AccessTokenManager::OnFetchComplete().
  //
  // (1) All the live Fetchers are created by this manager.
  //     This is because (1) all the live Fetchers are created by a live
  //     manager, as all the fetchers created by a manager are destructed in the
  //     manager's dtor.
  //
  // (2) All the uncompleted Fetchers created by this manager are recorded in
  //     |pending_fetchers_|.
  //     This is because (1) all the created Fetchers are added to
  //     |pending_fetchers_| (in method StartRequest()) and (2) method
  //     OnFetchComplete() is the only place where a Fetcher is erased from
  //     |pending_fetchers_|. Note no Fetcher is erased in method
  //     StartRequest().
  //
  // (3) Each of the Fetchers recorded in |pending_fetchers_| is mapped from
  //     its combination of client ID, account ID, and scope set. This is
  //     guaranteed by Fetcher creation in method StartRequest().
  //
  // When this method is called, |fetcher| is alive and uncompleted.
  // By (1), |fetcher| is created by this manager.
  // Then by (2), |fetcher| is recorded in |pending_fetchers_|.
  // Then by (3), |fetcher_| is mapped from its combination of client ID,
  // account ID, and scope set.
  RequestParameters request_param(
      fetcher->GetClientId(), fetcher->GetAccountId(), fetcher->GetScopeSet());

  const OAuth2AccessTokenConsumer::TokenResponse* entry =
      GetCachedTokenResponse(request_param);
  for (const base::WeakPtr<RequestImpl>& req : fetcher->waiting_requests()) {
    if (req) {
      for (auto& observer : diagnostics_observer_list_) {
        observer.OnFetchAccessTokenComplete(
            req->GetAccountId(), req->GetConsumerId(), fetcher->GetScopeSet(),
            fetcher->error(), entry ? entry->expiration_time : base::Time());
      }
    }
  }

  auto iter = pending_fetchers_.find(request_param);
  DCHECK(iter != pending_fetchers_.end());
  DCHECK_EQ(fetcher, iter->second.get());

  // The Fetcher deletes itself.
  iter->second.release();
  pending_fetchers_.erase(iter);
}

void OAuth2AccessTokenManager::CancelFetchers(
    std::vector<Fetcher*> fetchers_to_cancel) {
  for (Fetcher* pending_fetcher : fetchers_to_cancel)
    pending_fetcher->Cancel();
}