Pass the iid token to authenticate Instance-ID migration to FIS.

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -349,13 +349,23 @@ private String readExistingIidOrCreateFid(PersistedInstallationEntry prefs) {
   /** Registers the created Fid with FIS servers and update the persisted state. */
   private PersistedInstallationEntry registerFidWithServer(PersistedInstallationEntry prefs)
       throws IOException {
+
+    // Note: Default value of instanceIdMigrationAuth: null
+    String iidToken = null;
+
+    if (prefs.getFirebaseInstallationId().equals(iidStore.readIid())) {
+      // For a default firebase installation, read the stored star scoped iid token. This token
+      // will be used for authenticating Instance-ID when migrating to FIS.
+      iidToken = iidStore.readToken();
+    }
+
     InstallationResponse response =
         serviceClient.createFirebaseInstallation(
             /*apiKey= */ firebaseApp.getOptions().getApiKey(),
             /*fid= */ prefs.getFirebaseInstallationId(),
             /*projectID= */ firebaseApp.getOptions().getProjectId(),
             /*appId= */ getApplicationId(),
-            /* migration-header= */ null);
+            /* migration-header= */ iidToken);
 
     switch (response.getResponseCode()) {
       case OK:

firebase-installations/src/test/java/com/google/firebase/installations/FirebaseInstallationsTest.java

@@ -90,6 +90,8 @@ public class FirebaseInstallationsTest {
 
   public static final String TEST_INSTANCE_ID_1 = "ccccccccccc";
 
+  public static final String TEST_INSTANCE_ID_TOKEN_1 = "iid.token";
+
   public static final InstallationResponse TEST_INSTALLATION_RESPONSE =
       InstallationResponse.builder()
           .setUri("/projects/" + TEST_PROJECT_ID + "/installations/" + TEST_FID_1)
@@ -185,6 +187,7 @@ public void testGetId_noNetwork_noIid() throws Exception {
     when(mockBackend.generateAuthToken(anyString(), anyString(), anyString(), anyString()))
         .thenThrow(new IOException());
     when(mockIidStore.readIid()).thenReturn(null);
+    when(mockIidStore.readToken()).thenReturn(null);
 
     // Do the actual getId() call under test. Confirm that it returns a generated FID and
     // and that the FID was written to storage.
@@ -210,11 +213,16 @@ public void testGetId_noNetwork_noIid() throws Exception {
   @Test
   public void testGetId_noNetwork_iidPresent() throws Exception {
     when(mockBackend.createFirebaseInstallation(
-            anyString(), anyString(), anyString(), anyString(), any()))
+            TEST_API_KEY,
+            TEST_INSTANCE_ID_1,
+            TEST_PROJECT_ID,
+            TEST_APP_ID_1,
+            TEST_INSTANCE_ID_TOKEN_1))
         .thenThrow(new IOException());
     when(mockBackend.generateAuthToken(anyString(), anyString(), anyString(), anyString()))
         .thenThrow(new IOException());
     when(mockIidStore.readIid()).thenReturn(TEST_INSTANCE_ID_1);
+    when(mockIidStore.readToken()).thenReturn(TEST_INSTANCE_ID_TOKEN_1);
 
     // Do the actual getId() call under test. Confirm that it returns a generated FID and
     // and that the FID was written to storage.
@@ -340,8 +348,9 @@ public void testGetId_UnRegisteredId_IssueCreateIdCall() throws Exception {
   @Test
   public void testGetId_migrateIid_successful() throws Exception {
     when(mockIidStore.readIid()).thenReturn(TEST_INSTANCE_ID_1);
+    when(mockIidStore.readToken()).thenReturn(TEST_INSTANCE_ID_TOKEN_1);
     when(mockBackend.createFirebaseInstallation(
-            anyString(), anyString(), anyString(), anyString(), any()))
+            anyString(), anyString(), anyString(), anyString(), anyString()))
         .thenReturn(TEST_INSTALLATION_RESPONSE_WITH_IID);
 
     // Do the actual getId() call under test.
@@ -367,6 +376,7 @@ public void testGetId_migrateIid_successful() throws Exception {
   @Test
   public void testGetId_multipleCalls_sameFIDReturned() throws Exception {
     when(mockIidStore.readIid()).thenReturn(null);
+    when(mockIidStore.readToken()).thenReturn(null);
     when(mockBackend.createFirebaseInstallation(
             anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);