You can implement Single Sign-on for your Community by going to the Admin panel > Click Community Settings > scroll down to Access via OpenID Connect and click on Configure:
You will then be brought to a screen which will let you enable SSO, enforce the Single Sign-on login (so they users can ONLY login using SSO), key in your Client ID, Client Secret and Discovery URI.
Once you are done doing so, click Confirm.
Remember to test logging in on both the web and the mobile application!