Okta as IDP for Salesforce & Control Access to Another Custom Web Access

Let us see we use Okta as our enterprise IDP with Microsoft AD as Identity Store. We have configured Okta to support SSO, user provisioning and de-provisioning for our Salesforce installation. We also have another custom build web application. We want to use Okta for its SSO, user provisioning and de-provisioning as well. Our scenario is that only active Salesforce users can access the custom web application. What is the most efficient way to set it up?