fix permadiff on google_identity_platform_config.authorized_domains (#8740) (#15607)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/8740.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+identityplatform: fixed a permadiff on `authorized_domains` in `google_identity_platform_config` resource
+```

google/services/identityplatform/resource_identity_platform_config.go

@@ -50,6 +50,7 @@ func ResourceIdentityPlatformConfig() *schema.Resource {
 		Schema: map[string]*schema.Schema{
 			"authorized_domains": {
 				Type:        schema.TypeList,
+				Computed:    true,
 				Optional:    true,
 				Description: `List of domains authorized for OAuth redirects.`,
 				Elem: &schema.Schema{

google/services/identityplatform/resource_identity_platform_config_generated_test.go

@@ -101,3 +101,53 @@ resource "google_identity_platform_config" "default" {
 }
 `, context)
 }
+
+func TestAccIdentityPlatformConfig_identityPlatformConfigMinimalExample(t *testing.T) {
+	acctest.SkipIfVcr(t)
+	t.Parallel()
+
+	context := map[string]interface{}{
+		"org_id":        envvar.GetTestOrgFromEnv(t),
+		"billing_acct":  envvar.GetTestBillingAccountFromEnv(t),
+		"random_suffix": acctest.RandString(t, 10),
+	}
+
+	acctest.VcrTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.AccTestPreCheck(t) },
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccIdentityPlatformConfig_identityPlatformConfigMinimalExample(context),
+			},
+			{
+				ResourceName:      "google_identity_platform_config.default",
+				ImportState:       true,
+				ImportStateVerify: true,
+			},
+		},
+	})
+}
+
+func testAccIdentityPlatformConfig_identityPlatformConfigMinimalExample(context map[string]interface{}) string {
+	return acctest.Nprintf(`
+resource "google_project" "default" {
+  project_id = "tf-test-my-project-1%{random_suffix}"
+  name       = "tf-test-my-project-1%{random_suffix}"
+  org_id     = "%{org_id}"
+  billing_account =  "%{billing_acct}"
+  labels = {
+    firebase = "enabled"
+  }
+}
+
+resource "google_project_service" "identitytoolkit" {
+  project = google_project.default.project_id
+  service = "identitytoolkit.googleapis.com"
+}
+
+
+resource "google_identity_platform_config" "default" {
+  project = google_project.default.project_id
+}
+`, context)
+}