class Aws::Signers::V4

def canonical_headers(request)
  headers = []
  request.headers.each_pair do |k,v|
    k = k.downcase
    headers << [k,v] unless BLACKLIST_HEADERS.include?(k)
  end
  headers = headers.sort_by(&:first)
  headers.map{|k,v| "#{k}:#{canonical_header_value(v.to_s)}" }.join("\n")
end