Issue mozfr#400: add github pushes integration hook

Action needed on the beta server after this push:
- add secret key in config.ini
- create a file web/github_log.txt with the user www-data:www-data

We don't keep the log file in app/logs/ because we want to be able to access the date of the last update from GitHub into the browser

app/config/config.ini-dist

@@ -31,3 +31,6 @@ l10nwebservice = "https://l10n.mozilla-community.org/~flod/mozilla-l10n-query/"
 
 ; Flag to know if we are working in production more or development mode
 dev=false
+
+; Github secret key for continuous integration on Beta site
+github_key=putsecretkeyhere

web/github_hook.php

@@ -0,0 +1,72 @@
+<?php
+/* Webhook to update a repo for each push on GitHub. */
+
+date_default_timezone_set('Europe/Paris');
+
+// app variables
+$app_root = realpath(__DIR__ . '/../');
+$composer = $app_root . '/composer.phar';
+
+// git variables
+$branch = 'master';
+$header = 'HTTP_X_HUB_SIGNATURE';
+$secret = parse_ini_file($app_root . '/app/config/config.ini')['github_key'];
+
+// Logging function to output content to /github_log.txt
+function logHookResult($message , $success = false) {
+    $log_headers = "$message\n";
+    if (! $success) {
+        foreach ($_SERVER as $header => $value) {
+           $log_headers .= "$header: $value \n";
+        }
+    }
+    file_put_contents(__DIR__ . '/github_log.txt', $log_headers);
+}
+
+// CHECK: Download composer in the app root if it is not already there
+if (! file_exists($composer)) {
+    file_put_contents(
+        $composer,
+        file_get_contents('https://getcomposer.org/composer.phar')
+    );
+}
+
+if (isset($_SERVER[$header])) {
+    $validation = hash_hmac(
+        'sha1',
+        file_get_contents("php://input"),
+        $secret
+    );
+
+    if ($validation == explode('=', $_SERVER[$header])[1]) {
+        // Pull latest changes
+        exec("git checkout $branch ; git pull origin $branch");
+
+        // Install or update dependencies
+        if (file_exists($composer)) {
+            chdir($app_root);
+
+            // www-data does not have a HOME or COMPOSER_HOME, create one
+            if (! is_dir("{$app_root}/cache/.composer")) {
+                mkdir("{$app_root}/cache/.composer");
+            }
+
+            putenv("COMPOSER_HOME={$app_root}/cache/.composer");
+
+            if (file_exists($app_root . '/vendor')) {
+                exec("php {$composer} update > /dev/null 2>&1");
+            } else {
+                exec("php {$composer} install > /dev/null 2>&1");
+            }
+        }
+
+        // Delete cache
+        exec("rm {$app_root}/cache/*.cache > /dev/null 2>&1");
+
+        logHookResult('Last update: ' . date('d-m-Y H:i:s'), true);
+    } else {
+        logHookResult('Invalid GitHub secret');
+    }
+} else {
+    logHookResult("{$header} header missing, define a secret key for your project in GitHub");
+}