local base64 = require "base64"
local brute = require "brute"
local creds = require "creds"
local http = require "http"
local shortport = require "shortport"
local stdnse = require "stdnse"

description = [[
Performs brute force password guessing against HTTP proxy servers.
]]

---
-- @usage
-- nmap --script http-proxy-brute -p 8080 <host>
--
-- @output
-- PORT     STATE SERVICE
-- 8080/tcp open  http-proxy
-- | http-proxy-brute: 
-- |   Accounts
-- |     patrik:12345 - Valid credentials
-- |   Statistics
-- |_    Performed 6 guesses in 2 seconds, average tps: 3
--
-- @args http-proxy-brute.url sets an alternative URL to use when brute forcing
--       (default: http://scanme.insecure.org)
-- @args http-proxy-brute.method changes the HTTP method to use when performing
--       brute force guessing (default: HEAD)

author = "Patrik Karlsson"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

-- maybe the script does not need to be in the external category
-- as most request should not "leave" the proxy.
categories = {"brute", "intrusive", "external"}


portrule = shortport.port_or_service({8123,3128,8000,8080},{'polipo','squid-http','http-proxy'})

local arg_url 		= stdnse.get_script_args(SCRIPT_NAME .. '.url') or 'http://scanme.nmap.org/'
local arg_method	= stdnse.get_script_args(SCRIPT_NAME .. '.method') or "HEAD"

Driver = {
	
	new = function(self, host, port)
		local o = { host = host, port = port }
		setmetatable(o, self)
		self.__index = self
		return o
	end,
	
	connect = function( self )
		return true
	end,
	
	login = function( self, username, password )

		-- the http library does not yet support proxy authentication, so let's
		-- do what's necessary here.
	    local header = { ["Proxy-Authorization"] = "Basic " .. base64.enc(username .. ":" .. password) }
		local response = http.generic_request(self.host, self.port, arg_method, arg_url, { header = header, bypass_cache = true } )
		
		-- if we didn't get a 407 error, assume the credentials
		-- were correct. we should probably do some more checks here
		if ( response.status ~= 407 ) then
			return true, brute.Account:new( username, password, creds.State.VALID)
		end
		
		return false, brute.Error:new( "Incorrect password" )
	end,
	
	disconnect = function( self ) 
		return true
	end,
}

-- checks whether the proxy really needs authentication and that the
-- authentication mechanism can be handled by our script, currently only
-- BASIC authentication is supported.
local function checkProxy(host, port, url)
	local response = http.generic_request(host, port, arg_method, url, { bypass_cache = true })

	if ( response.status ~= 407 ) then
		return false, "Proxy server did not require authentication"
	end

	local proxy_auth = response.header["proxy-authenticate"]
	if ( not(proxy_auth) ) then
		return false, "No proxy authentication header was found"
	end
	
	local challenges = http.parse_www_authenticate(proxy_auth)
	
	for _, challenge in ipairs(challenges) do
		if ( "Basic" == challenge.scheme ) then
			return true
		end
	end
	return false, "The authentication scheme wasn't supported"
end

action = function(host, port)

	local status, err = checkProxy(host, port, arg_url)
	if ( not(status) ) then
		return ("\n  ERROR: %s"):format(err)
	end

	local engine = brute.Engine:new(Driver, host, port)
	engine.options.script_name = SCRIPT_NAME
	local result
	status, result = engine:start()

	return result
end
