The growth of public and private cloud services, and the proliferation of open source cloud solutions is un- deniable. At the same time, new security features are being developed to provide a stronger confidence of end users and to improve the user experience. Examples of these features are advanced/extensible authentication mechanisms, Single Sign-On (SSO) and Identity Federation. This work introduces a novel approach to provide these features to cloud services, by taking advantage of well-known and widely deployed protocols. On the one hand, Kerberos, providing an advanced authentication framework and a native SSO mechanism. On the other, the AAA protocols (such as RADIUS or Diameter) providing widely deployed network access identity federations, such as eduroam. The proposed solution allows the end user to bootstrap fresh valid authentication credentials to access cloud services in a visited organization from a previous network authentication process, backed up by a AAA identity federation. Moreover, it does not imply modifications to the current standards. A proof-of-concept has been been implemented to validate the feasibility of this proposal.