Pour l'instant mon programme ressemble à ça mais je n'arrive pas à ce que la led s'allume ou s'éteigne en fonction...
Mais le moniteur série affiche bien le "on" ou le "off" qui change 
/**
- BasicHTTPClient.ino
-
- Created on: 24.05.2015
-
*/
#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>
#include <ESP8266HTTPClient.h>
#define USE_SERIAL Serial
ESP8266WiFiMulti WiFiMulti;
void setup() {
USE_SERIAL.begin(115200);
// USE_SERIAL.setDebugOutput(true);
USE_SERIAL.println();
USE_SERIAL.println();
USE_SERIAL.println();
for(uint8_t t = 4; t > 0; t--) {
USE_SERIAL.printf("[SETUP] WAIT %d...\n", t);
USE_SERIAL.flush();
delay(1000);
}
WiFi.mode(WIFI_STA);
WiFiMulti.addAP("gougeon", "F11F1E8EB1");
pinMode(LED_BUILTIN, OUTPUT);
}
void loop() {
// wait for WiFi connection
if((WiFiMulti.run() == WL_CONNECTED)) {
HTTPClient http;
USE_SERIAL.print("[HTTP] begin...\n");
// configure traged server and url
//http.begin("https://192.168.1.12/test.html", "7a 9c f4 db 40 d3 62 5a 6e 21 bc 5c cc 66 c8 3e a1 45 59 38"); //HTTPS
http.begin("http://homeuh.nexgate.ch/p1.txt"); //HTTP
USE_SERIAL.print("[HTTP] GET...\n");
// start connection and send HTTP header
int httpCode = http.GET();
// httpCode will be negative on error
if(httpCode > 0) {
// HTTP header has been send and Server response header has been handled
USE_SERIAL.printf("[HTTP] GET... code: %d\n", httpCode);
// file found at server
if(httpCode == HTTP_CODE_OK) {
String content = http.getString();
USE_SERIAL.println("(" + content + ")");
if (content = "on") {
delay(200);
digitalWrite(LED_BUILTIN, 1);
Serial.println("LED ON");
}
if (content != "on") {
delay(200);
digitalWrite(LED_BUILTIN, 0);
Serial.println("LED OFF");
}
}
} else {
USE_SERIAL.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());
}
http.end();
}
delay(10000);
}