Methods and apparatus are provided for authenticating a remote service to another service on behalf of a user. A user client authorizes a remote application client to perform one or more actions with a server on behalf of the user client. The user client provides one or more keys to a remote authentication service; receives an identifier of the remote application client, where the remote authentication client is remote from the server; and notifies the remote authentication service that the remote application client is authorized to obtain a response from the remote authentication service regarding a challenge from the server, where the response is based on at least one of the one or more keys stored by the remote authentication service on behalf of the user client. The remote application client provides a challenge that is received from a server that the remote application client is attempting to access for the user client and an identifier of the user client to a remote authentication service and receives a response to the challenge from the remote authentication service, wherein the response is based on one or more keys stored by the remote authentication service on behalf of the user client.