Whilst there certainly are great OSS solutions most big-ish corps already have Active Directory. You can setup ADFS to do SAML for SSO or you can use Azure AD w

Whilst there certainly are great OSS solutions most big-ish corps already have Active Directory. You can setup ADFS to do SAML for SSO or you can use Azure AD which already has all that out of the box. If you aren't a big-ish corp then yeah, there are tons of OSS ways of doing IdP that fit your specific tastes etc.