https://developers.google.com/identity/protocols/oauth2
Pushes me to the "Google Auth Platform", but I can't find anything on provisioning a client or what seems to be required "Branding" through Google's Terraform provider.
You are probably looking for these two resources:
google_iap_brand - https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/iap_brand
google_iap_client - https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/iap_client
However, Google recently announced deprecation of the API that these resources use (https://cloud.google.com/iap/docs/deprecations/migrate-oauth-client).
I got in touch with Google Cloud support, and they confirmed that these two resources will no longer work after July 2025.
Here is full response that I got from the support: https://github.com/hashicorp/terraform-provider-google/issues/21378#issuecomment-2653497606