You can enable an external identity provider using SAML 2.0.
Follow the steps below to start the SAML 2.0 SSO configuration:
Navigate to the Setup Home page.
On the left, go to Manage > Company Preferences.
Click on the Security Settings tab.
Click the Edit button.
Under Single Sign-On Settings, check the Single Sign-On (SAML) Enabled box.
Click Save.
Scroll back to the Single Sign-On Settings section and click on the Manage SAML Provider Settings link.
Click New and fill in the required information.
Refer to the Help Document for more information.