/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#ifndef GRPCPP_SECURITY_CREDENTIALS_H
#define GRPCPP_SECURITY_CREDENTIALS_H

#include <map>
#include <memory>
#include <vector>

#include <grpc/grpc_security_constants.h>
#include <grpcpp/channel.h>
#include <grpcpp/impl/codegen/client_interceptor.h>
#include <grpcpp/impl/codegen/grpc_library.h>
#include <grpcpp/security/auth_context.h>
#include <grpcpp/security/tls_credentials_options.h>
#include <grpcpp/support/channel_arguments.h>
#include <grpcpp/support/status.h>
#include <grpcpp/support/string_ref.h>

struct grpc_call;

namespace grpc {
class CallCredentials;
class SecureCallCredentials;
class SecureChannelCredentials;
class ChannelCredentials;

std::shared_ptr<Channel> CreateCustomChannel(
    const grpc::string& target,
    const std::shared_ptr<grpc::ChannelCredentials>& creds,
    const grpc::ChannelArguments& args);

namespace experimental {
std::shared_ptr<grpc::Channel> CreateCustomChannelWithInterceptors(
    const grpc::string& target,
    const std::shared_ptr<grpc::ChannelCredentials>& creds,
    const grpc::ChannelArguments& args,
    std::vector<
        std::unique_ptr<grpc::experimental::ClientInterceptorFactoryInterface>>
        interceptor_creators);

/// Builds XDS Credentials.
std::shared_ptr<ChannelCredentials> XdsCredentials(
    const std::shared_ptr<ChannelCredentials>& fallback_creds);
}  // namespace experimental

/// A channel credentials object encapsulates all the state needed by a client
/// to authenticate with a server for a given channel.
/// It can make various assertions, e.g., about the client’s identity, role
/// for all the calls on that channel.
///
/// \see https://grpc.io/docs/guides/auth.html
class ChannelCredentials : private grpc::GrpcLibraryCodegen {
 public:
  ChannelCredentials();
  ~ChannelCredentials() override;

 protected:
  friend std::shared_ptr<ChannelCredentials> CompositeChannelCredentials(
      const std::shared_ptr<ChannelCredentials>& channel_creds,
      const std::shared_ptr<CallCredentials>& call_creds);

  // TODO(yashykt): We need this friend declaration mainly for access to
  // AsSecureCredentials(). Once we are able to remove insecure builds from gRPC
  // (and also internal dependencies on the indirect method of creating a
  // channel through credentials), we would be able to remove this.
  friend std::shared_ptr<ChannelCredentials> grpc::experimental::XdsCredentials(
      const std::shared_ptr<ChannelCredentials>& fallback_creds);

  virtual SecureChannelCredentials* AsSecureCredentials() = 0;

 private:
  friend std::shared_ptr<grpc::Channel> CreateCustomChannel(
      const grpc::string& target,
      const std::shared_ptr<grpc::ChannelCredentials>& creds,
      const grpc::ChannelArguments& args);

  friend std::shared_ptr<grpc::Channel>
  grpc::experimental::CreateCustomChannelWithInterceptors(
      const grpc::string& target,
      const std::shared_ptr<grpc::ChannelCredentials>& creds,
      const grpc::ChannelArguments& args,
      std::vector<std::unique_ptr<
          grpc::experimental::ClientInterceptorFactoryInterface>>
          interceptor_creators);

  virtual std::shared_ptr<Channel> CreateChannelImpl(
      const grpc::string& target, const ChannelArguments& args) = 0;

  // This function should have been a pure virtual function, but it is
  // implemented as a virtual function so that it does not break API.
  virtual std::shared_ptr<Channel> CreateChannelWithInterceptors(
      const grpc::string& /*target*/, const ChannelArguments& /*args*/,
      std::vector<std::unique_ptr<
          grpc::experimental::ClientInterceptorFactoryInterface>>
      /*interceptor_creators*/) {
    return nullptr;
  }

  // TODO(yashkt): This is a hack that is needed since InsecureCredentials can
  // not use grpc_channel_credentials internally and should be removed after
  // insecure builds are removed from gRPC.
  virtual bool IsInsecure() const { return false; }
};

/// A call credentials object encapsulates the state needed by a client to
/// authenticate with a server for a given call on a channel.
///
/// \see https://grpc.io/docs/guides/auth.html
class CallCredentials : private grpc::GrpcLibraryCodegen {
 public:
  CallCredentials();
  ~CallCredentials() override;

  /// Apply this instance's credentials to \a call.
  virtual bool ApplyToCall(grpc_call* call) = 0;
  virtual grpc::string DebugString() {
    return "CallCredentials did not provide a debug string";
  }

 protected:
  friend std::shared_ptr<ChannelCredentials> CompositeChannelCredentials(
      const std::shared_ptr<ChannelCredentials>& channel_creds,
      const std::shared_ptr<CallCredentials>& call_creds);

  friend std::shared_ptr<CallCredentials> CompositeCallCredentials(
      const std::shared_ptr<CallCredentials>& creds1,
      const std::shared_ptr<CallCredentials>& creds2);

  virtual SecureCallCredentials* AsSecureCredentials() = 0;
};

/// Options used to build SslCredentials.
struct SslCredentialsOptions {
  /// The buffer containing the PEM encoding of the server root certificates. If
  /// this parameter is empty, the default roots will be used.  The default
  /// roots can be overridden using the \a GRPC_DEFAULT_SSL_ROOTS_FILE_PATH
  /// environment variable pointing to a file on the file system containing the
  /// roots.
  grpc::string pem_root_certs;

  /// The buffer containing the PEM encoding of the client's private key. This
  /// parameter can be empty if the client does not have a private key.
  grpc::string pem_private_key;

  /// The buffer containing the PEM encoding of the client's certificate chain.
  /// This parameter can be empty if the client does not have a certificate
  /// chain.
  grpc::string pem_cert_chain;
};

// Factories for building different types of Credentials The functions may
// return empty shared_ptr when credentials cannot be created. If a
// Credentials pointer is returned, it can still be invalid when used to create
// a channel. A lame channel will be created then and all rpcs will fail on it.

/// Builds credentials with reasonable defaults.
///
/// \warning Only use these credentials when connecting to a Google endpoint.
/// Using these credentials to connect to any other service may result in this
/// service being able to impersonate your client for requests to Google
/// services.
std::shared_ptr<ChannelCredentials> GoogleDefaultCredentials();

/// Builds SSL Credentials given SSL specific options
std::shared_ptr<ChannelCredentials> SslCredentials(
    const SslCredentialsOptions& options);

/// Builds credentials for use when running in GCE
///
/// \warning Only use these credentials when connecting to a Google endpoint.
/// Using these credentials to connect to any other service may result in this
/// service being able to impersonate your client for requests to Google
/// services.
std::shared_ptr<CallCredentials> GoogleComputeEngineCredentials();

constexpr long kMaxAuthTokenLifetimeSecs = 3600;

/// Builds Service Account JWT Access credentials.
/// json_key is the JSON key string containing the client's private key.
/// token_lifetime_seconds is the lifetime in seconds of each Json Web Token
/// (JWT) created with this credentials. It should not exceed
/// \a kMaxAuthTokenLifetimeSecs or will be cropped to this value.
std::shared_ptr<CallCredentials> ServiceAccountJWTAccessCredentials(
    const grpc::string& json_key,
    long token_lifetime_seconds = kMaxAuthTokenLifetimeSecs);

/// Builds refresh token credentials.
/// json_refresh_token is the JSON string containing the refresh token along
/// with a client_id and client_secret.
///
/// \warning Only use these credentials when connecting to a Google endpoint.
/// Using these credentials to connect to any other service may result in this
/// service being able to impersonate your client for requests to Google
/// services.
std::shared_ptr<CallCredentials> GoogleRefreshTokenCredentials(
    const grpc::string& json_refresh_token);

/// Builds access token credentials.
/// access_token is an oauth2 access token that was fetched using an out of band
/// mechanism.
///
/// \warning Only use these credentials when connecting to a Google endpoint.
/// Using these credentials to connect to any other service may result in this
/// service being able to impersonate your client for requests to Google
/// services.
std::shared_ptr<CallCredentials> AccessTokenCredentials(
    const grpc::string& access_token);

/// Builds IAM credentials.
///
/// \warning Only use these credentials when connecting to a Google endpoint.
/// Using these credentials to connect to any other service may result in this
/// service being able to impersonate your client for requests to Google
/// services.
std::shared_ptr<CallCredentials> GoogleIAMCredentials(
    const grpc::string& authorization_token,
    const grpc::string& authority_selector);

/// Combines a channel credentials and a call credentials into a composite
/// channel credentials.
std::shared_ptr<ChannelCredentials> CompositeChannelCredentials(
    const std::shared_ptr<ChannelCredentials>& channel_creds,
    const std::shared_ptr<CallCredentials>& call_creds);

/// Combines two call credentials objects into a composite call credentials.
std::shared_ptr<CallCredentials> CompositeCallCredentials(
    const std::shared_ptr<CallCredentials>& creds1,
    const std::shared_ptr<CallCredentials>& creds2);

/// Credentials for an unencrypted, unauthenticated channel
std::shared_ptr<ChannelCredentials> InsecureChannelCredentials();

/// User defined metadata credentials.
class MetadataCredentialsPlugin {
 public:
  virtual ~MetadataCredentialsPlugin() {}

  /// If this method returns true, the Process function will be scheduled in
  /// a different thread from the one processing the call.
  virtual bool IsBlocking() const { return true; }

  /// Type of credentials this plugin is implementing.
  virtual const char* GetType() const { return ""; }

  /// Gets the auth metatada produced by this plugin.
  /// The fully qualified method name is:
  /// service_url + "/" + method_name.
  /// The channel_auth_context contains (among other things), the identity of
  /// the server.
  virtual grpc::Status GetMetadata(
      grpc::string_ref service_url, grpc::string_ref method_name,
      const grpc::AuthContext& channel_auth_context,
      std::multimap<grpc::string, grpc::string>* metadata) = 0;

  virtual grpc::string DebugString() {
    return "MetadataCredentialsPlugin did not provide a debug string";
  }
};

std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
    std::unique_ptr<MetadataCredentialsPlugin> plugin);

namespace experimental {

/// Options for creating STS Oauth Token Exchange credentials following the IETF
/// draft https://tools.ietf.org/html/draft-ietf-oauth-token-exchange-16.
/// Optional fields may be set to empty string. It is the responsibility of the
/// caller to ensure that the subject and actor tokens are refreshed on disk at
/// the specified paths.
struct StsCredentialsOptions {
  grpc::string token_exchange_service_uri;  // Required.
  grpc::string resource;                    // Optional.
  grpc::string audience;                    // Optional.
  grpc::string scope;                       // Optional.
  grpc::string requested_token_type;        // Optional.
  grpc::string subject_token_path;          // Required.
  grpc::string subject_token_type;          // Required.
  grpc::string actor_token_path;            // Optional.
  grpc::string actor_token_type;            // Optional.
};

grpc::Status StsCredentialsOptionsFromJson(const std::string& json_string,
                                           StsCredentialsOptions* options);

/// Creates STS credentials options from the $STS_CREDENTIALS environment
/// variable. This environment variable points to the path of a JSON file
/// comforming to the schema described above.
grpc::Status StsCredentialsOptionsFromEnv(StsCredentialsOptions* options);

std::shared_ptr<CallCredentials> StsCredentials(
    const StsCredentialsOptions& options);

std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
    std::unique_ptr<MetadataCredentialsPlugin> plugin,
    grpc_security_level min_security_level);

/// Options used to build AltsCredentials.
struct AltsCredentialsOptions {
  /// service accounts of target endpoint that will be acceptable
  /// by the client. If service accounts are provided and none of them matches
  /// that of the server, authentication will fail.
  std::vector<grpc::string> target_service_accounts;
};

/// Builds ALTS Credentials given ALTS specific options
std::shared_ptr<ChannelCredentials> AltsCredentials(
    const AltsCredentialsOptions& options);

/// Builds Local Credentials.
std::shared_ptr<ChannelCredentials> LocalCredentials(
    grpc_local_connect_type type);

/// Builds TLS Credentials given TLS options.
std::shared_ptr<ChannelCredentials> TlsCredentials(
    const TlsChannelCredentialsOptions& options);

}  // namespace experimental
}  // namespace grpc

#endif  // GRPCPP_SECURITY_CREDENTIALS_H