client.py

import hmac
import time
import requests

SHARED_KEY = "hemligt"
BASE_URL = "https://myserver.com:8443/?duration={0}&token={1}"

def compute_auth():
    auth = hmac.new(
        SHARED_KEY, 
        str(int(time.time()))
    )
    return auth.hexdigest()

def run(duration):
    token = compute_auth()
    duration = BASE_URL.format(duration, token)
    r = requests.get(duration, verify=False)

# run for 9 seconds
run(9)

get_temp.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import requests

def get_temperature():
	data = requests.get("https://wttr.in/karlskrona", verify=False).text
  # sort of messy data with escape chars... not suitable for regexp.
	start = "\x1b[0m \x1b[38;5;"
	end = "\x1b"
	temp = data.split(start)[1].split(end)[0].split("\x1b[0m")
	return temp[0].split("m")[1]

def get_duration():
	try:
		temp = get_temperature()
	except:
		temp = 14

	# define function... lets do this from empirical observations.

irrigate.py

import ssl
import time
import RPi.GPIO as GPIO
import BaseHTTPServer, SimpleHTTPServer
import urlparse
import hmac

PORT = 18 # PIN on Raspberry Pi
SHARED_KEY = "hemligt"

def pump(duration):
    GPIO.setmode(GPIO.BCM)
    GPIO.setwarnings(False)
    GPIO.setup(PORT, GPIO.OUT)
    GPIO.output(PORT, GPIO.HIGH)
    time.sleep(duration)
    GPIO.output(PORT, GPIO.LOW)


class IrrigationHandler(BaseHTTPServer.BaseHTTPRequestHandler):

    def compute_auth(self, ctime):
        auth = hmac.new(SHARED_KEY, str(ctime))
        return auth.hexdigest()

    def authenticate(self, token):
        ctime = int(time.time())
        for i in range(-10, 10):
            if self.compute_auth(ctime + i) == token:
                return True
        return False

    def do_GET(self):
        o = urlparse.urlparse(self.path)
        data = urlparse.parse_qs(o.query)
        if not self.authenticate(data.get("token")[0]): # yep, will stack trace if not given
            self.send_response(503)
            self.end_headers()
            return
        self.send_response(200)
        self.send_header("Content-type", "text/html")
        self.end_headers()
        try:
            duration = data.get("duration")[0]
            pump(int(duration))
        except:
            pump(9)

httpd = BaseHTTPServer.HTTPServer(
    ('0.0.0.0', 8443), IrrigationHandler
)
httpd.socket = ssl.wrap_socket(
    httpd.socket, certfile='./cert.pem', server_side=True
)
httpd.serve_forever()