def set_hsts_headers!(headers)
      opts = { :expires => 31536000, :subdomains => true, :preload => false }
      opts.merge!(@options[:hsts]) if @options[:hsts].is_a? Hash
      value  = "max-age=#{opts[:expires]}"
      value += "; includeSubDomains" if opts[:subdomains]
      value += "; preload" if opts[:preload]
      headers.merge!({ 'Strict-Transport-Security' => value })
    end
def set_hsts_headers!(headers)
      opts = { :expires => 31536000, :subdomains => true, :preload => false }
      opts.merge!(@options[:hsts]) if @options[:hsts].is_a? Hash
      value  = "max-age=#{opts[:expires]}"
      value += "; includeSubDomains" if opts[:subdomains]
      value += "; preload" if opts[:preload]
      headers.merge!({ 'Strict-Transport-Security' => value })
    end
see http://en.wikipedia.org/wiki/Strict_Transport_Security