The SSO feature was introduced with Microsoft Office SharePoint Portal Server 2003 and improved with SharePoint Server 2007.
SSO allowed one to retrieve information from external systems such as ERPs and CRMs by just signing in once through SharePoint.
Secure Store Service contains a physical database and runs on an application server.
The Secure Store Service accepts and decrypts security tokens provided by the applications in order to identify the application ID.
Applications That Use Secure Store Service
Business Connectivity Services
PowerPivot for SharePoint
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