When integrating a SP that supports both SAML and OIDC with Salesforce, the use case that is the determining factor when choosing OIDC or SAML is whether the SP needs to perform API calls back to Salesforce on behalf of the user after the user logs in to the service provider. OIDC is a protocol that allows users to authorize an external application to access Salesforce resources on their behalf. OIDC provides an access token that can be used to call Salesforce APIs. SAML is a protocol that allows users to authenticate andauthorize with an external identity provider and access Salesforce resources. SAML does not provide an access token, but only a sessionID that can be used for web-based access. Therefore, if the SP needs to perform API calls back to Salesforce, OIDC is the preferred choice over SAML. References: OpenID Connect, SAML, Authorize Apps with OAuth