diff --git a/package.json b/package.json
index db9de5f..21271ad 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "apple-signin",
-  "version": "1.0.6",
+  "version": "1.0.9",
   "description": "Node.JS wrapper around Sign In with Apple REST API",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
diff --git a/readme.md b/readme.md
index a237708..689b43c 100644
--- a/readme.md
+++ b/readme.md
@@ -29,7 +29,7 @@ Start "Sign in with Apple" flow by redirecting user to the authorization URL.
 const appleSignin = require("apple-signin");
 
 const options = {
-    clientId: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
+    clientID: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
     redirectUri: "http://localhost:3000/auth/apple/callback",
     state: "123", // optional, An unguessable random string. It is primarily used to protect against CSRF attacks.
     scope: "email" // optional, default value is "email".
@@ -50,14 +50,14 @@ More detail can be found in [Apple docs](https://developer.apple.com/documentati
 ```javascript
 
 const clientSecret = appleSignin.getClientSecret({
-    clientId: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
+    clientID: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
     teamId: "teamId", // Apple Developer Team ID.
     privateKeyPath: "/var/www/app/AuthKey_XXX.p8", // path to private key associated with your client ID.
     keyIdentifier: "XXX" // identifier of the private key.    
 });
 
 const options = {
-    clientId: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
+    clientID: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
     redirectUri: "http://localhost:3000/auth/apple/callback", // use the same value which you passed to authorisation URL.
     clientSecret: clientSecret
 };
@@ -82,7 +82,7 @@ Result of ```getAuthorizationToken``` command is a JSON object representing Appl
 
 ### 3. Verify token signature and get unique user's identifier
 ```javascript
-appleSignin.verifyIdToken(tokenResponse.id_token).then(result => {
+appleSignin.verifyIdToken(tokenResponse.id_token, clientID).then(result => {
     const userAppleId = result.sub;
 }).catch(error => {
     // Token is not verified
@@ -93,14 +93,14 @@ appleSignin.verifyIdToken(tokenResponse.id_token).then(result => {
 ```javascript
 
 const clientSecret = appleSignin.getClientSecret({
-    clientId: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
+    clientID: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
     teamId: "teamId", // Apple Developer Team ID.
     privateKeyPath: "/var/www/app/AuthKey_XXX.p8", // path to private key associated with your client ID.
     keyIdentifier: "XXX" // identifier of the private key.    
 });
 
 const options = {
-    clientId: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
+    clientID: "com.gotechmakers.auth.client", // identifier of Apple Service ID.
     clientSecret: clientSecret
 };
  
diff --git a/source/index.js b/source/index.js
index f50e549..2b52612 100644
--- a/source/index.js
+++ b/source/index.js
@@ -6,6 +6,7 @@ const request = require('request-promise-native');
 
 const ENDPOINT_URL = 'https://appleid.apple.com';
 const DEFAULT_SCOPE = 'email';
+const TOKEN_ISSUER = 'https://appleid.apple.com';
 
 const getAuthorizationUrl = (options = {}) => {
   if (!options.clientID) throw Error('clientID is empty');
@@ -29,11 +30,11 @@ const getAuthorizationUrl = (options = {}) => {
 };
 
 const getClientSecret = options => {
-  if (!options.clientID) throw Error('clientID is empty');
-  if (!options.teamId) throw Error('teamId is empty');
-  if (!options.keyIdentifier) throw Error('keyIdentifier is empty');
-  if (!options.privateKeyPath) throw Error('privateKeyPath is empty');
-  if (!fs.existsSync(options.privateKeyPath)) throw Error("Can't find private key");
+  if (!options.clientID) throw new Error('clientID is empty');
+  if (!options.teamId) throw new Error('teamId is empty');
+  if (!options.keyIdentifier) throw new Error('keyIdentifier is empty');
+  if (!options.privateKeyPath) throw new Error('privateKeyPath is empty');
+  if (!fs.existsSync(options.privateKeyPath)) throw new Error("Can't find private key");
 
   const timeNow = Math.floor(Date.now() / 1000);
 
@@ -52,9 +53,9 @@ const getClientSecret = options => {
 };
 
 const getAuthorizationToken = async (code, options) => {
-  if (!options.clientID) throw Error('clientID is empty');
-  if (!options.redirectUri) throw Error('redirectUri is empty');
-  if (!options.clientSecret) throw Error('clientSecret is empty');
+  if (!options.clientID) throw new Error('clientID is empty');
+  if (!options.redirectUri) throw new Error('redirectUri is empty');
+  if (!options.clientSecret) throw new Error('clientSecret is empty');
 
   const url = new URL(ENDPOINT_URL);
   url.pathname = '/auth/token';
@@ -72,8 +73,8 @@ const getAuthorizationToken = async (code, options) => {
 };
 
 const refreshAuthorizationToken = async (refreshToken, options) => {
-  if (!options.clientID) throw Error('clientID is empty');
-  if (!options.clientSecret) throw Error('clientSecret is empty');
+  if (!options.clientID) throw new Error('clientID is empty');
+  if (!options.clientSecret) throw new Error('clientSecret is empty');
 
   const url = new URL(ENDPOINT_URL);
   url.pathname = '/auth/token';
@@ -101,9 +102,15 @@ const getApplePublicKey = async () => {
   return pubKey.exportKey(['public']);
 };
 
-const verifyIdToken = async idToken => {
-  const pubKey = await getApplePublicKey();
-  return jwt.verify(idToken, pubKey, { algorithms: 'RS256' });
+const verifyIdToken = async (idToken, clientID) => {
+  const applePublicKey = await getApplePublicKey();
+  const jwtClaims = jwt.verify(idToken, applePublicKey, { algorithms: 'RS256' });
+
+  if (jwtClaims.iss !== TOKEN_ISSUER) throw new Error('id token not issued by correct OpenID provider - expected: ' + TOKEN_ISSUER + ' | from: ' + jwtClaims.iss);
+  if (clientID !== undefined && jwtClaims.aud !== clientID) throw new Error('aud parameter does not include this client - is: ' + jwtClaims.aud + '| expected: ' + clientID);
+  if (jwtClaims.exp < (Date.now() / 1000)) throw new Error('id token has expired');
+
+  return jwtClaims;
 };