SAP is encouraging all SuccessFactors customers to upgrade the login method to SAP IAS (SAP Cloud Platform Identity Authentication Service). For SuccessFactors customers before Q3 2019, they are releasing this upgrade as the part of Release new features and for SuccessFactors customers who are coming onboard after Q3 2019 there is already pre-integration between SuccessFactors and IAS.
The whole idea of this IAS upgrade is to replace the basic SF login with IAS login.
SAP’s idea is to make IAS as central IDP (Identity provisioning or user store) for accessing all SAP Cloud applications. For this the journey has started and they are suggesting customers to migrate from SF basic login to IAS. Some of the new SAP Cloud products like SAP Analytics needs SF IAS login. SAP Analytics does not work with SF Basic Login. So this upgrade to IAS suggestion is applicable to all SF customers who are using SF with Basic login and SF with Corporate SSO (For ex. Microsoft AD).
Customers who are not using Corporate SSO: For the customers who are not using corporate SSO and using just SF basic login with SF url and SF user id and pwd, when such customer upgrade to IAS their basic SF login is replaced by IAS login and there is no change in SF user id. Customer still uses same SF url and user id to login. Below diagram is for reference to this scenario
Customers who are using Corporate SSO: For the customers who are using corporate SSO (For example if a customer is using Microsoft ADFS/Azure AD as corporate AD and SSO is enabled with SuccessFactors) who is using AD credentials as login to get into SF Application, when such customer upgrade to IAS, they have to redo SSO configuration between IAS and Corporate AD. Below diagram is for reference to this scenario
Conclusion: Upgrading SuccessFactors Login to IAS integrates your SF landscape into IAS. In future if you decide to implement any other cloud application of SAP like SAP Analytics, SAP new careers site integration, etc., then your SF landscape is capable of doing such implementation as IAS is prerequisite for implementing such solutions.
Below is example of IAS landscape with Microsoft Azure AD
Hope this information is helpful !