Universal containers wants to implement single Sign-on for a salesforce org using an external identityprovider...

Service-provider-initiated SSO is required to support deep linking, which is the ability to direct users to a specific page within Salesforce from a different app. With service-provider-initiated SSO, the user requests a resource from Salesforce (the service provider), which then redirects the user to the identity provider for authentication. After the user is authenticated, the identity provider sends a SAML response back to Salesforce, which then grants access to the requested resource. Web server OAuth SSO flow is used for OAuth 2.0 authentication, not SAML. Identity-provider-initiated SSO is when the user logs in to the identity provider first and then selects a service provider to access. Start URL on identity provider is not a type of authentication flow,but a parameter that can be used to specify the landing page after SSO. References: Certification - Identity and Access Management Architect - Trailhead, Deep Linking, Single Sign On Deep Linking - Salesforce Developer Community