token_cache.hpp

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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
 
#pragma once
 
#include <azure/core/credentials/credentials.hpp>
 
#include <chrono>
#include <functional>
#include <map>
#include <memory>
#include <shared_mutex>
#include <string>
#include <tuple>
 
namespace Azure { namespace Identity { namespace _detail {
  class TokenCache
#if !defined(_azure_TESTING_BUILD)
      final
#endif
  {
#if !defined(_azure_TESTING_BUILD)
  private:
#else
  protected:
#endif
    // A test hook that gets invoked before cache write lock gets acquired.
    virtual void OnBeforeCacheWriteLock() const {};
 
    // A test hook that gets invoked before item write lock gets acquired.
    virtual void OnBeforeItemWriteLock() const {};
 
    struct CacheKey
    {
      std::string Scope;
      std::string TenantId;
    };
 
    struct CacheKeyComparator
    {
      bool operator()(CacheKey const& lhs, CacheKey const& rhs) const
      {
        return std::tie(lhs.Scope, lhs.TenantId) < std::tie(rhs.Scope, rhs.TenantId);
      }
    };
 
    struct CacheValue
    {
      Core::Credentials::AccessToken AccessToken;
      std::shared_timed_mutex ElementMutex;
    };
 
    mutable std::map<CacheKey, std::shared_ptr<CacheValue>, CacheKeyComparator> m_cache;
    mutable std::shared_timed_mutex m_cacheMutex;
 
  private:
    TokenCache(TokenCache const&) = delete;
    TokenCache& operator=(TokenCache const&) = delete;
 
    // Checks cache element if cached value should be reused. Caller should be holding ElementMutex.
    static bool IsFresh(
        std::shared_ptr<CacheValue> const& item,
        DateTime::duration minimumExpiration,
        std::chrono::system_clock::time_point now);
 
    // Gets item from cache, or creates it, puts into cache, and returns.
    std::shared_ptr<CacheValue> GetOrCreateValue(
        CacheKey const& key,
        DateTime::duration minimumExpiration) const;
 
  public:
    TokenCache() = default;
    ~TokenCache() = default;
 
    Core::Credentials::AccessToken GetToken(
        std::string const& scopeString,
        std::string const& tenantId,
        DateTime::duration minimumExpiration,
        std::function<Core::Credentials::AccessToken()> const& getNewToken) const;
  };
}}} // namespace Azure::Identity::_detail