Add SobanleClient token cache and login

app/libs/SobanleClient.js

+"use strict";
+var config = require(__config_path + "/config");
+var ApiRequest = require("./ApiRequest");
+
+var tokenCache = { token: null, expiresAt: 0 };
+
+function login(callback) {
+  var url = config.sobanle.base_url + "/login";
+  ApiRequest.postOtherUrl(url, { login: config.sobanle.username, password: config.sobanle.password }, function (err, body) {
+    if (err) {
+      return callback(err);
+    }
+    if (!body || !body.access_token) {
+      return callback(new Error("SOBANLE_LOGIN_FAILED"));
+    }
+    tokenCache.token = body.access_token;
+    var expiresInMs = (body.expires_in || 0) * 1000;
+    // Refresh a bit early to avoid racing a near-expiry token. Headroom scales
+    // with the token's own TTL (capped at 60s) rather than a flat 60s, so a
+    // short-TTL token isn't already "expired" the instant it's cached.
+    var earlyRefreshMs = Math.min(60000, expiresInMs * 0.1);
+    tokenCache.expiresAt = Date.now() + expiresInMs - earlyRefreshMs;
+    callback(null, body.access_token);
+  });
+}
+exports.login = login;
+
+function getToken(callback) {
+  if (tokenCache.token && Date.now() < tokenCache.expiresAt) {
+    return callback(null, tokenCache.token);
+  }
+  exports.login(callback);
+}
+exports.getToken = getToken;
+
+exports._resetTokenCacheForTest = function () {
+  tokenCache.token = null;
+  tokenCache.expiresAt = 0;
+};