Hi Mike,
As Digital ID is OpenID compliant, it can be easily integrated with our WordPress OAuth client SSO plugin and it will allow your users to login into WordPress using their Digital ID.
Also, you mentioned that you have Gravity Forms and you want to identify users before filling out the form.
This is possible and we have worked on similar case for our customers.
Whenever users tries to access any form, we can ask users to login with DigitalID first and the information received from DigitalID can be populated in the gravity form.
I will also send you an email to discuss it further.
Let me know if you have any questions.