Write Firebase Token to Auth instance during exchange_token API (#9060)

* Write Firebase Token to Auth instance

* yarn run format

* Fix unit test and run yarn docgen:all

* Address comments

Author: mansisampat

docs-devsite/_toc.yaml

@@ -246,6 +246,8 @@ toc:
     path: /docs/reference/js/auth.emulatorconfig.md
   - title: FacebookAuthProvider
     path: /docs/reference/js/auth.facebookauthprovider.md
+  - title: FirebaseToken
+    path: /docs/reference/js/auth.firebasetoken.md
   - title: GithubAuthProvider
     path: /docs/reference/js/auth.githubauthprovider.md
   - title: GoogleAuthProvider

docs-devsite/auth.auth.md

@@ -28,6 +28,7 @@ export interface Auth
 |  [config](./auth.auth.md#authconfig) | [Config](./auth.config.md#config_interface) | The [Config](./auth.config.md#config_interface) used to initialize this instance. |
 |  [currentUser](./auth.auth.md#authcurrentuser) | [User](./auth.user.md#user_interface) \| null | The currently signed-in user (or null). |
 |  [emulatorConfig](./auth.auth.md#authemulatorconfig) | [EmulatorConfig](./auth.emulatorconfig.md#emulatorconfig_interface) \| null | The current emulator configuration (or null). |
+|  [firebaseToken](./auth.auth.md#authfirebasetoken) | [FirebaseToken](./auth.firebasetoken.md#firebasetoken_interface) \| null | The token response initialized via [exchangeToken()](./auth.md#exchangetoken_b6b1871) endpoint. |
 |  [languageCode](./auth.auth.md#authlanguagecode) | string \| null | The [Auth](./auth.auth.md#auth_interface) instance's language code. |
 |  [name](./auth.auth.md#authname) | string | The name of the app associated with the <code>Auth</code> service instance. |
 |  [settings](./auth.auth.md#authsettings) | [AuthSettings](./auth.authsettings.md#authsettings_interface) | The [Auth](./auth.auth.md#auth_interface) instance's settings. |
@@ -87,6 +88,18 @@ The current emulator configuration (or null).
 readonly emulatorConfig: EmulatorConfig | null;
 ```
 
+## Auth.firebaseToken
+
+The token response initialized via [exchangeToken()](./auth.md#exchangetoken_b6b1871) endpoint.
+
+This field is only supported for [Auth](./auth.auth.md#auth_interface) instance that have defined [TenantConfig](./auth.tenantconfig.md#tenantconfig_interface)<!-- -->.
+
+<b>Signature:</b>
+
+```typescript
+readonly firebaseToken: FirebaseToken | null;
+```
+
 ## Auth.languageCode
 
 The [Auth](./auth.auth.md#auth_interface) instance's language code.

docs-devsite/auth.firebasetoken.md

@@ -0,0 +1,40 @@
+Project: /docs/reference/js/_project.yaml
+Book: /docs/reference/_book.yaml
+page_type: reference
+
+{% comment %}
+DO NOT EDIT THIS FILE!
+This is generated by the JS SDK team, and any local changes will be
+overwritten. Changes should be made in the source code at
+https://github.com/firebase/firebase-js-sdk
+{% endcomment %}
+
+# FirebaseToken interface
+<b>Signature:</b>
+
+```typescript
+export interface FirebaseToken 
+```
+
+## Properties
+
+|  Property | Type | Description |
+|  --- | --- | --- |
+|  [expirationTime](./auth.firebasetoken.md#firebasetokenexpirationtime) | number |  |
+|  [token](./auth.firebasetoken.md#firebasetokentoken) | string |  |
+
+## FirebaseToken.expirationTime
+
+<b>Signature:</b>
+
+```typescript
+readonly expirationTime: number;
+```
+
+## FirebaseToken.token
+
+<b>Signature:</b>
+
+```typescript
+readonly token: string;
+```

docs-devsite/auth.md

@@ -118,6 +118,7 @@ Firebase Authentication
 |  [ConfirmationResult](./auth.confirmationresult.md#confirmationresult_interface) | A result from a phone number sign-in, link, or reauthenticate call. |
 |  [Dependencies](./auth.dependencies.md#dependencies_interface) | The dependencies that can be used to initialize an [Auth](./auth.auth.md#auth_interface) instance. |
 |  [EmulatorConfig](./auth.emulatorconfig.md#emulatorconfig_interface) | Configuration of Firebase Authentication Emulator. |
+|  [FirebaseToken](./auth.firebasetoken.md#firebasetoken_interface) |  |
 |  [IdTokenResult](./auth.idtokenresult.md#idtokenresult_interface) | Interface representing ID token result obtained from [User.getIdTokenResult()](./auth.user.md#usergetidtokenresult)<!-- -->. |
 |  [MultiFactorAssertion](./auth.multifactorassertion.md#multifactorassertion_interface) | The base class for asserting ownership of a second factor. |
 |  [MultiFactorError](./auth.multifactorerror.md#multifactorerror_interface) | The error thrown when the user needs to provide a second factor to sign in successfully. |