gistfile1.rb

require 'net/http'

class ServerProxy
  def self.call(env)
    if env["PATH_INFO"] =~ /^\/server_proxy/
      request = Rack::Request.new(env)
      params = request.params
      
      Net::HTTP.start(params["service_url"]) {|http|
                      req = Net::HTTP::Get.new(params["service_path"])
                      req.basic_auth params['username'], params['password'] 
                      response = http.request(req)
                      @server_response = response.body
                      @server_code = response.code
                      @server_content_type = response.content_type
                    }

      [@server_code, {"Content-Type" => @server_content_type}, [@server_response]]
    else
      [404, {"Content-Type" => "text/html"}, ["Not Found"]]
    end
  end
end

Thank you! It works great.