diff --git a/auth.js b/auth.js
index 843fcb0..061aaa2 100644
--- a/auth.js
+++ b/auth.js
@@ -1,13 +1,21 @@
 const fetch = require('node-fetch');
+const querystring = require('querystring');
 
 // Timeout other API calls after this number of seconds
 const API_TIMEOUT_SECONDS = 40;
 
 // We want to look like a browser
 const USER_AGENT_STRING =
-    'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36';
+    'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.120 Safari/537.36';
 
-const JWT_ISSUE_URL = 'https://nestauthproxyservice-pa.googleapis.com/v1/issue_jwt';
+// Client ID of the Nest iOS application
+const CLIENT_ID =
+    '733249279899-1gpkq9duqmdp55a7e5lft1pr2smumdla.apps.googleusercontent.com';
+
+const JWT_ISSUE_URL =
+    'https://nestauthproxyservice-pa.googleapis.com/v1/issue_jwt';
+
+const TOKEN_URL = 'https://oauth2.googleapis.com/token';
 
 /**
  * Use the provided configuration to authenticate with Google and retrieve a JWT for
@@ -20,19 +28,21 @@ const JWT_ISSUE_URL = 'https://nestauthproxyservice-pa.googleapis.com/v1/issue_j
  * @param apiKey
  * @returns {Promise<{refresh: (function(): Promise<{refresh, expiry, token}>), expiry: Date, token: string}>}
  */
-const googleAuth = async (issueToken, cookies, apiKey) => {
+const googleAuth = async refreshToken => {
     // Request an access token
-    const tokenResult = await fetch(issueToken, {
-        method: 'GET',
+    const tokenResult = await fetch(TOKEN_URL, {
+        method: 'POST',
         redirect: 'follow',
         timeout: API_TIMEOUT_SECONDS * 1000,
         headers: {
-            'Sec-Fetch-Mode': 'cors',
+            'Content-Type': 'application/x-www-form-urlencoded',
             'User-Agent': USER_AGENT_STRING,
-            'X-Requested-With': 'XmlHttpRequest',
-            Referer: 'https://accounts.google.com/o/oauth2/iframe',
-            cookie: cookies,
         },
+        body: querystring.stringify({
+            refresh_token: refreshToken,
+            client_id: CLIENT_ID,
+            grant_type: 'refresh_token',
+        }),
     });
     const tokenJSON = await tokenResult.json();
     const googleAccessToken = tokenJSON.access_token;
@@ -51,9 +61,8 @@ const googleAuth = async (issueToken, cookies, apiKey) => {
         headers: {
             Authorization: 'Bearer ' + googleAccessToken,
             'User-Agent': USER_AGENT_STRING,
-            'x-goog-api-key': apiKey,
             Referer: 'https://home.nest.com',
-        }
+        },
     });
     const jwtJSON = await jwtResult.json();
     const googleJWT = jwtJSON.jwt;
@@ -70,4 +79,4 @@ const googleAuth = async (issueToken, cookies, apiKey) => {
     };
 };
 
-module.exports = googleAuth;
\ No newline at end of file
+module.exports = googleAuth;
diff --git a/package-lock.json b/package-lock.json
index 811c270..f58bafe 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -41,6 +41,11 @@
       "integrity": "sha512-OeHeMc0JhFE9idD4ZdtNibzY0+TPHSpSSb9h8FqtP+YnoZZ1sl8Vc9b1sasjfymH3SonAF4QcA2+mzHPhMvIiw==",
       "dev": true
     },
+    "querystring": {
+      "version": "0.2.1",
+      "resolved": "https://registry.npmjs.org/querystring/-/querystring-0.2.1.tgz",
+      "integrity": "sha512-wkvS7mL/JMugcup3/rMitHmd9ecIGd2lhFhK9N3UUQ450h66d1r3Y9nvXzQAW1Lq+wyx61k/1pfKS5KuKiyEbg=="
+    },
     "ts-protoc-gen": {
       "version": "0.11.0",
       "resolved": "https://registry.npmjs.org/ts-protoc-gen/-/ts-protoc-gen-0.11.0.tgz",
diff --git a/package.json b/package.json
index 8e6ceaf..de18c8c 100644
--- a/package.json
+++ b/package.json
@@ -31,6 +31,7 @@
   "dependencies": {
     "google-protobuf": "^3.10.0",
     "node-fetch": "^2.6.0",
+    "querystring": "^0.2.1",
     "uuid": "^3.3.3"
   },
   "devDependencies": {