Adding Node.js Auth Token Claims

Adding Admin Node.js code snippets
for https://firebase.google.com/docs/auth/admin/create-custom-tokens

Author: jenperson

auth/create_custom_tokens.js

@@ -0,0 +1,38 @@
+// Initialize the Admin app with the default appication credentials
+// [START initialize_sdk_with_default_config]
+admin.initializeApp();
+// [END initialize_sdk_with_default_config]
+
+// Initialize the Admin app by providing a service accoune key
+// [START initialize_sdk_with_service_account_id]
+admin.initializeApp({
+  serviceAccountId: 'my-client-id@my-project-id.iam.gserviceaccount.com',
+});
+// [END initialize_sdk_with_service_account_id]
+
+// [START custom_token]
+var uid = "some-uid";
+
+admin.auth().createCustomToken(uid)
+  .then(function(customToken) {
+    // Send token back to client
+  })
+  .catch(function(error) {
+    console.log("Error creating custom token:", error);
+  });
+// [END custom_token]
+
+// [START custom_token_with_claims]
+var uid = "some-uid";
+var additionalClaims = {
+  premiumAccount: true
+};
+
+admin.auth().createCustomToken(uid, additionalClaims)
+  .then(function(customToken) {
+    // Send token back to client
+  })
+  .catch(function(error) {
+    console.log("Error creating custom token:", error);
+  });
+// [END custom_token_with_claims]