Google has a great OAuth configuration article with steps to enable SSO. When you get to Create Credentials, here are details that will set you up with everything you need to finish the task in the DNSFilter dashboard. 

1. Select Web Application as the Application Type
2. Enter the App Name 
3. Under Authorized JavaScript origins, select Add URI
   a. Enter https://auth.dnsfilter.com 
4. Under Authorized redirect URIs, select Add URI
   a. Enter https://auth.dnsfilter.com/login/callback 
5. Select Create
6. Copy (or select Download JSON) the Client ID and Client secret
7. Format the Discovery URL to match Google Workspace's OpenID URL 
   e.g. https://accounts.google.com/.well-known/openid-configuration

Navigate to the DNSFilter dashboard and follow the instruction to complete the SSO setup.