# File lib/aws/core/client.rb, line 699
        def signature_version version, service_signing_name = nil
          define_method(:sign_request) do |req|
            @signer ||= begin
              signer_class = AWS::Core::Signers.const_get(version)
              signer_args = (version == :Version4) ?
                [credential_provider, service_signing_name, req.region] :
                [credential_provider]
              signer_class.new(*signer_args)
            end
            @signer.sign_request(req)
            req
          end
        end