How to allow supplier login with username/password, but keep SSO only for employees?

We are looking to implement the Supplier Portal functionality and we would like to know how to enable supplier login with username password, and SSO for employees.

We have enabled federated SSO only login for our internal users (employees). SSO is configured with non-chooser login option.

For the Supplier Portal, suppliers would receive a web link to connect to our instance. However, with the current SSO setup, they cannot login with user/password. We need a solution for supplier login, whilst keeping SSO only for employees.

I've found the following documents and threads on CCC:

1)  https://community.oracle.com/customerconnect/discussion/620247/how-to-enable-supplier-login-with-username-password-and-sso-for-employees