Merge pull request #100972 from MicrosoftDocs/release-ga-immersive-reader

Release ga immersive reader

Author: huypub

articles/cognitive-services/immersive-reader/azure-active-directory-authentication.md

@@ -0,0 +1,76 @@
+---
+title: "Cache the authentication token"
+titleSuffix: Azure Cognitive Services
+description: This article will show you how to cache the authentication token.
+author: metanMSFT
+manager: guillasi
+
+ms.service: cognitive-services
+ms.subservice: immersive-reader
+ms.topic: conceptual
+ms.date: 01/14/2020
+ms.author: metan
+---
+
+# How to cache the authentication token
+
+This article demonstrates how to cache the authentication token in order to improve performance of your application.
+
+## Using ASP.NET
+
+Import the **Microsoft.IdentityModel.Clients.ActiveDirectory** NuGet package, which is used to acquire a token. Next, use the following code to acquire an `AuthenticationResult`, using the authentication values you got when you [created the Immersive Reader resource](./how-to-create-immersive-reader.md).
+
+```csharp
+private async Task<AuthenticationResult> GetTokenAsync()
+{
+    AuthenticationContext authContext = new AuthenticationContext($"https://login.windows.net/{TENANT_ID}");
+    ClientCredential clientCredential = new ClientCredential(CLIENT_ID, CLIENT_SECRET);
+    AuthenticationResult authResult = await authContext.AcquireTokenAsync("https://cognitiveservices.azure.com/", clientCredential);
+    return authResult;
+}
+```
+
+The `AuthenticationResult` object has an `AccessToken` property which is the actual token you will use when launching the Immersive Reader using the SDK. It also has an `ExpiresOn` property which denotes when the token will expire. Before launching the Immersive Reader, you can check whether the token has expired, and acquire a new token only if it has expired.
+
+## Using Node.JS
+
+Add the [**request**](https://www.npmjs.com/package/request) npm package to your project. Use the following code to acquire a token, using the authentication values you got when you [created the Immersive Reader resource](./how-to-create-immersive-reader.md).
+
+```javascript
+router.get('/token', function(req, res) {
+    request.post(
+        {
+            headers: { 'content-type': 'application/x-www-form-urlencoded' },
+            url: `https://login.windows.net/${TENANT_ID}/oauth2/token`,
+            form: {
+                grant_type: 'client_credentials',
+                client_id: CLIENT_ID,
+                client_secret: CLIENT_SECRET,
+                resource: 'https://cognitiveservices.azure.com/'
+            }
+        },
+        function(err, resp, json) {
+            const result = JSON.parse(json);
+            return res.send({
+                access_token: result.access_token,
+                expires_on: result.expires_on
+            });
+        }
+    );
+});
+```
+
+The `expires_on` property is the date and time at which the token expires, expressed as the number of seconds since January 1, 1970 UTC. Use this value to determine whether your token has expired before attempting to acquire a new one.
+
+```javascript
+async function getToken() {
+    if (Date.now() / 1000 > CREDENTIALS.expires_on) {
+        CREDENTIALS = await refreshCredentials();
+    }
+    return CREDENTIALS.access_token;
+}
+```
+
+## Next steps
+
+* Explore the [Immersive Reader SDK Reference](./reference.md)