Disclosed is a method performed by an authentication server for authentication of users requesting access to a restricted data resource from a communication device, the authentication server being situated in the restricted data resource. After checking that a username and password received from a communication device matches a stored username and password, the authentication server sends, using the RADIUS protocol, a request to the communication device to enter an approver ID. After receiving an approver ID from the communication device in response to the request, via the RADIUS protocol, the authentication server sends an approval request including user ID to an approver device indicated by the approver ID, and if the approver approves the request, the authentication server receives an accept to the approval request and grants the user access to the restricted data resource.