Identity as a Service (IDaaS) is an authentication infrastructure that is built, hosted and managed by a third-party service provider. IDaaS can be thought of as single sign-on (SSO) for the cloud.

An IDaaS for the enterprise is typically purchased as a subscription-based managed service. A cloud service provider may also host applications for a fee and provide subscribers with role-based access to specific applications or even entire virtualized desktops through a secure portal.

Source: https://searchmobilecomputing.techtarget.com/definition/identity-as-a-Service-IDaaS

• AWS: https://aws.amazon.com/blogs/security/introducing-aws-single-sign-on/
• Azure: https://blogs.technet.microsoft.com/cbernier/2014/09/02/identity-as-a-service-idaas/