text: //
  // Copyright 2020 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.
  //
  #include <grpc/support/port_platform.h>
  
  #include "src/core/lib/security/credentials/external/aws_request_signer.h"
  
  #include "absl/strings/ascii.h"
  #include "absl/strings/escaping.h"
  #include "absl/strings/str_format.h"
  #include "absl/strings/str_join.h"
  #include "absl/strings/str_split.h"
  #include "absl/time/clock.h"
  #include "absl/time/time.h"
  
  #include <openssl/hmac.h>
  #include <openssl/sha.h>
  
  namespace grpc_core {
  
  namespace {
  
  const char kAlgorithm[] = "AWS4-HMAC-SHA256";
  const char kDateFormat[] = "%a, %d %b %E4Y %H:%M:%S %Z";
  const char kXAmzDateFormat[] = "%Y%m%dT%H%M%SZ";
  
  void SHA256(const std::string& str, unsigned char out[SHA256_DIGEST_LENGTH]) {
    SHA256_CTX sha256;
    SHA256_Init(&sha256);
    SHA256_Update(&sha256, str.c_str(), str.size());
    SHA256_Final(out, &sha256);
  }
  
  std::string SHA256Hex(const std::string& str) {
    unsigned char hash[SHA256_DIGEST_LENGTH];
    SHA256(str, hash);
    std::string hash_str(reinterpret_cast<char const*>(hash),
                         SHA256_DIGEST_LENGTH);
    return absl::BytesToHexString(hash_str);
  }
  
  std::string HMAC(const std::string& key, const std::string& msg) {
    unsigned int len;
    unsigned char digest[EVP_MAX_MD_SIZE];
    HMAC(EVP_sha256(), key.c_str(), key.length(),
         (const unsigned char*)msg.c_str(), msg.length(), digest, &len);
    return std::string(digest, digest + len);
  }
  
  }  // namespace
  
  AwsRequestSigner::AwsRequestSigner(
      std::string access_key_id, std::string secret_access_key, std::string token,
      std::string method, std::string url, std::string region,
      std::string request_payload,
      std::map<std::string, std::string> additional_headers, grpc_error** error)
      : access_key_id_(std::move(access_key_id)),
        secret_access_key_(std::move(secret_access_key)),
        token_(std::move(token)),
        method_(std::move(method)),
        region_(std::move(region)),
        request_payload_(std::move(request_payload)),
        additional_headers_(std::move(additional_headers)) {
    auto amz_date_it = additional_headers_.find("x-amz-date");
    auto date_it = additional_headers_.find("date");
    if (amz_date_it != additional_headers_.end() &&
        date_it != additional_headers_.end()) {
      *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
          "Only one of {date, x-amz-date} can be specified, not both.");
      return;
    }
    if (amz_date_it != additional_headers_.end()) {
      static_request_date_ = amz_date_it->second;
    } else if (date_it != additional_headers_.end()) {
      absl::Time request_date;
      std::string err_str;
      if (!absl::ParseTime(kDateFormat, date_it->second, &request_date,
                           &err_str)) {
        *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(err_str.c_str());
        return;
      }
      static_request_date_ =
          absl::FormatTime(kXAmzDateFormat, request_date, absl::UTCTimeZone());
    }
    url_ = grpc_uri_parse(url, false);
    if (url_ == nullptr) {
      *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Invalid Aws request url.");
      return;
    }
  }
  
  AwsRequestSigner::~AwsRequestSigner() { grpc_uri_destroy(url_); }
  
  std::map<std::string, std::string> AwsRequestSigner::GetSignedRequestHeaders() {
    std::string request_date_full;
    if (!static_request_date_.empty()) {
      if (!request_headers_.empty()) {
        return request_headers_;
      }
      request_date_full = static_request_date_;
    } else {
      absl::Time request_date = absl::Now();
      request_date_full =
          absl::FormatTime(kXAmzDateFormat, request_date, absl::UTCTimeZone());
    }
    std::string request_date_short = request_date_full.substr(0, 8);
    // TASK 1: Create a canonical request for Signature Version 4
    // https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
    std::vector<absl::string_view> canonical_request_vector;
    // 1. HTTPRequestMethod
    canonical_request_vector.emplace_back(method_);
    canonical_request_vector.emplace_back("\n");
    // 2. CanonicalURI
  
    canonical_request_vector.emplace_back(*url_->path == '\0' ? "/" : url_->path);
    canonical_request_vector.emplace_back("\n");
    // 3. CanonicalQueryString
    canonical_request_vector.emplace_back(url_->query);
    canonical_request_vector.emplace_back("\n");
    // 4. CanonicalHeaders
    if (request_headers_.empty()) {
      request_headers_.insert({"host", url_->authority});
      if (!token_.empty()) {
        request_headers_.insert({"x-amz-security-token", token_});
      }
      for (const auto& header : additional_headers_) {
        request_headers_.insert(
            {absl::AsciiStrToLower(header.first), header.second});
      }
    }
    if (additional_headers_.find("date") == additional_headers_.end()) {
      request_headers_["x-amz-date"] = request_date_full;
    }
    std::vector<absl::string_view> canonical_headers_vector;
    for (const auto& header : request_headers_) {
      canonical_headers_vector.emplace_back(header.first);
      canonical_headers_vector.emplace_back(":");
      canonical_headers_vector.emplace_back(header.second);
      canonical_headers_vector.emplace_back("\n");
    }
    std::string canonical_headers = absl::StrJoin(canonical_headers_vector, "");
    canonical_request_vector.emplace_back(canonical_headers);
    canonical_request_vector.emplace_back("\n");
    // 5. SignedHeaders
    std::vector<absl::string_view> signed_headers_vector;
    for (const auto& header : request_headers_) {
      signed_headers_vector.emplace_back(header.first);
    }
    std::string signed_headers = absl::StrJoin(signed_headers_vector, ";");
    canonical_request_vector.emplace_back(signed_headers);
    canonical_request_vector.emplace_back("\n");
    // 6. RequestPayload
    std::string hashed_request_payload = SHA256Hex(request_payload_);
    canonical_request_vector.emplace_back(hashed_request_payload);
    std::string canonical_request = absl::StrJoin(canonical_request_vector, "");
    // TASK 2: Create a string to sign for Signature Version 4
    // https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html
    std::vector<absl::string_view> string_to_sign_vector;
    // 1. Algorithm
    string_to_sign_vector.emplace_back("AWS4-HMAC-SHA256");
    string_to_sign_vector.emplace_back("\n");
    // 2. RequestDateTime
    string_to_sign_vector.emplace_back(request_date_full);
    string_to_sign_vector.emplace_back("\n");
    // 3. CredentialScope
    std::pair<absl::string_view, absl::string_view> host_parts =
        absl::StrSplit(url_->authority, absl::MaxSplits('.', 1));
    std::string service_name(host_parts.first);
    std::string credential_scope = absl::StrFormat(
        "%s/%s/%s/aws4_request", request_date_short, region_, service_name);
    string_to_sign_vector.emplace_back(credential_scope);
    string_to_sign_vector.emplace_back("\n");
    // 4. HashedCanonicalRequest
    std::string hashed_canonical_request = SHA256Hex(canonical_request);
    string_to_sign_vector.emplace_back(hashed_canonical_request);
    std::string string_to_sign = absl::StrJoin(string_to_sign_vector, "");
    // TASK 3: Task 3: Calculate the signature for AWS Signature Version 4
    // https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html
    // 1. Derive your signing key.
    std::string date = HMAC("AWS4" + secret_access_key_, request_date_short);
    std::string region = HMAC(date, region_);
    std::string service = HMAC(region, service_name);
    std::string signing = HMAC(service, "aws4_request");
    // 2. Calculate the signature.
    std::string signature_str = HMAC(signing, string_to_sign);
    std::string signature = absl::BytesToHexString(signature_str);
    // TASK 4: Add the signature to the HTTP request
    // https://docs.aws.amazon.com/general/latest/gr/sigv4-add-signature-to-request.html
    std::string authorization_header = absl::StrFormat(
        "%s Credential=%s/%s, SignedHeaders=%s, Signature=%s", kAlgorithm,
        access_key_id_, credential_scope, signed_headers, signature);
    request_headers_["Authorization"] = authorization_header;
    return request_headers_;
  }
  
  }  // namespace grpc_core
  