Authentication and Authorisation Infrastructures (AAIs) are gaining momentum throughout the Internet. Solutions have been proposed for various scenarios among them academia, GRID computing, company networks, and above all eCommerce applications. Products and concepts vary in architecture, security features, target group, and usability containing different strengths and weaknesses. In addition security needs have changed in communication and business processes. Security on the internet is no longer defined as only security measures for an eCommerce provider against an untrustworthy customer but also vice versa. Consequently, privacy, data canniness, and security are demands in this area. The authors define criteria for an eCommerce provider federation using an AAI with a maximum of privacy and flexibility. The criteria is derived concentrating on b2c eCommerce applications fulfilling the demands. In addition to best practices found, XACML policies and an attribute infrastructure ar...