Store OpenID cookie secret in settings db and make it unique per instance

src/settings.js

@@ -7,6 +7,9 @@ exports = module.exports = {
     getTimeZone,
     setTimeZone,
 
+    getCookieSecret,
+    setCookieSecret,
+
     getCloudronName,
     setCloudronName,
 
@@ -119,6 +122,7 @@ exports = module.exports = {
     // strings
     AUTOUPDATE_PATTERN_KEY: 'autoupdate_pattern',
     TIME_ZONE_KEY: 'time_zone',
+    CLOUDRON_COOKIE_SECRET_KEY: 'cookie_secret',
     CLOUDRON_NAME_KEY: 'cloudron_name',
     LANGUAGE_KEY: 'language',
     CLOUDRON_ID_KEY: 'cloudron_id',
@@ -175,6 +179,7 @@ const gDefaults = (function () {
     const result = { };
     result[exports.AUTOUPDATE_PATTERN_KEY] = cron.DEFAULT_AUTOUPDATE_PATTERN;
     result[exports.TIME_ZONE_KEY] = 'UTC';
+    result[exports.CLOUDRON_COOKIE_SECRET_KEY] = '';
     result[exports.CLOUDRON_NAME_KEY] = 'Cloudron';
     result[exports.DYNAMIC_DNS_KEY] = false;
     result[exports.IPV6_CONFIG_KEY] = {
@@ -332,6 +337,19 @@ async function getTimeZone() {
     return tz;
 }
 
+async function getCookieSecret() {
+    const secret = await get(exports.CLOUDRON_COOKIE_SECRET_KEY);
+    return secret;
+}
+
+async function setCookieSecret(secret) {
+    assert.strictEqual(typeof secret, 'string');
+
+    if (!secret) throw new BoxError(BoxError.BAD_FIELD, 'secret is empty');
+
+    await set(exports.CLOUDRON_COOKIE_SECRET_KEY, secret);
+}
+
 async function getCloudronName() {
     const name = await get(exports.CLOUDRON_NAME_KEY);
     if (name === null) return gDefaults[exports.CLOUDRON_NAME_KEY];