class Aws::Plugins::Sign::SignatureV4

def sign(context)
  req = context.http_request
  apply_authtype(context, req)
  reset_signature(req)
  apply_clock_skew(context, req)
  # compute the signature
  begin
    signature = @signer.sign_request(
      http_method: req.http_method,
      url: req.endpoint,
      headers: req.headers,
      body: req.body
    )
  rescue Aws::Sigv4::Errors::MissingCredentialsError
    # Necessary for when credentials is explicitly set to nil
    raise Aws::Errors::MissingCredentialsError
  end
  # apply signature headers
  req.headers.update(signature.headers)
  # add request metadata with signature components for debugging
  context[:canonical_request] = signature.canonical_request
  context[:string_to_sign] = signature.string_to_sign
end