class Aws::Sigv4::Signer

def sign_request(request)
  creds, _ = fetch_credentials
  http_method = extract_http_method(request)
  url = extract_url(request)
  Signer.normalize_path(url) if @normalize_path
  headers = downcase_headers(request[:headers])
  datetime = headers['x-amz-date']
  datetime ||= Time.now.utc.strftime("%Y%m%dT%H%M%SZ")
  date = datetime[0,8]
  content_sha256 = headers['x-amz-content-sha256']
  content_sha256 ||= sha256_hexdigest(request[:body] || '')
  sigv4_headers = {}
  sigv4_headers['host'] = headers['host'] || host(url)
  sigv4_headers['x-amz-date'] = datetime
  if creds.session_token && !@omit_session_token
    if @signing_algorithm == 'sigv4-s3express'.to_sym
      sigv4_headers['x-amz-s3session-token'] = creds.session_token
    else
      sigv4_headers['x-amz-security-token'] = creds.session_token
    end
  end
  sigv4_headers['x-amz-content-sha256'] ||= content_sha256 if @apply_checksum_header
  if @signing_algorithm == :sigv4a && @region && !@region.empty?
    sigv4_headers['x-amz-region-set'] = @region
  end
  headers = headers.merge(sigv4_headers) # merge so we do not modify given headers hash
  algorithm = sts_algorithm
  # compute signature parts
  creq = canonical_request(http_method, url, headers, content_sha256)
  sts = string_to_sign(datetime, creq, algorithm)
  sig =
    if @signing_algorithm == :sigv4a
      asymmetric_signature(creds, sts)
    else
      signature(creds.secret_access_key, date, sts)
    end
  algorithm = sts_algorithm
  # apply signature
  sigv4_headers['authorization'] = [
    "#{algorithm} Credential=#{credential(creds, date)}",
    "SignedHeaders=#{signed_headers(headers)}",
    "Signature=#{sig}",
  ].join(', ')
  # skip signing the session token, but include it in the headers
  if creds.session_token && @omit_session_token
    sigv4_headers['x-amz-security-token'] = creds.session_token
  end
  # Returning the signature components.
  Signature.new(
    headers: sigv4_headers,
    string_to_sign: sts,
    canonical_request: creq,
    content_sha256: content_sha256,
    signature: sig
  )
end