Clarify the default behavior for IAP OAuth client fields in backend services (#13145) (#21536)

[upstream:1d4d34ef3ddae618d6e2f97b7c27c7a87606cc09]

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

Author: modular-magician

.changelog/13145.txt

@@ -0,0 +1,3 @@
+```release-note:none
+
+```

google/services/compute/resource_compute_backend_service.go

@@ -633,11 +633,12 @@ For internal load balancing, a URL to a HealthCheck resource must be specified i
 				Set: tpgresource.SelfLinkRelativePathHash,
 			},
 			"iap": {
-				Type:        schema.TypeList,
-				Computed:    true,
-				Optional:    true,
-				Description: `Settings for enabling Cloud Identity Aware Proxy`,
-				MaxItems:    1,
+				Type:     schema.TypeList,
+				Computed: true,
+				Optional: true,
+				Description: `Settings for enabling Cloud Identity Aware Proxy.
+If OAuth client is not set, the Google-managed OAuth client is used.`,
+				MaxItems: 1,
 				Elem: &schema.Resource{
 					Schema: map[string]*schema.Schema{
 						"enabled": {

google/services/compute/resource_compute_region_backend_service.go

@@ -560,11 +560,12 @@ or serverless NEG as a backend.`,
 				Set: tpgresource.SelfLinkRelativePathHash,
 			},
 			"iap": {
-				Type:        schema.TypeList,
-				Computed:    true,
-				Optional:    true,
-				Description: `Settings for enabling Cloud Identity Aware Proxy`,
-				MaxItems:    1,
+				Type:     schema.TypeList,
+				Computed: true,
+				Optional: true,
+				Description: `Settings for enabling Cloud Identity Aware Proxy.
+If OAuth client is not set, Google-managed OAuth client is used.`,
+				MaxItems: 1,
 				Elem: &schema.Resource{
 					Schema: map[string]*schema.Schema{
 						"enabled": {

website/docs/r/compute_backend_service.html.markdown

@@ -507,7 +507,8 @@ The following arguments are supported:
 
 * `iap` -
   (Optional)
-  Settings for enabling Cloud Identity Aware Proxy
+  Settings for enabling Cloud Identity Aware Proxy.
+  If OAuth client is not set, the Google-managed OAuth client is used.
   Structure is [documented below](#nested_iap).
 
 * `ip_address_selection_policy` -

website/docs/r/compute_region_backend_service.html.markdown

@@ -515,7 +515,8 @@ The following arguments are supported:
 
 * `iap` -
   (Optional)
-  Settings for enabling Cloud Identity Aware Proxy
+  Settings for enabling Cloud Identity Aware Proxy.
+  If OAuth client is not set, Google-managed OAuth client is used.
   Structure is [documented below](#nested_iap).
 
 * `ip_address_selection_policy` -