Some of the major SSO challenges that organizations should expect are:
Challenges integrating applications: One of the main challenges during the implementation of SSO is integration with various systems and applications. Legacy technology with obsolete architecture that lives on-premises or homegrown applications that don’t work with typical identity standards can often be challenging to connect. The best way to ensure interoperability is to choose an extensible identity vendor that supports open standards as well as many out-of-the-box integrations.
Accessibility challenges: When the single sign-on service is down, access to all connected sites may also go down. The provider's vulnerability to any interruptions becomes yours. For this reason, organizations need to exercise a lot of care when choosing an SSO vendor. An ideal system should be exceptionally reliable—99.99% uptime is ideal. You should also develop backup plans in case of outages.
Data Breaches: Should a hacker steal a user’s credentials, all of that user’s applications would be compromised because of the reliance on one password for access. However, you can significantly reduce this risk by requiring your users to follow good password practices, educating about the common signs of phishing and implementing MFA.