An authentication system combines device credential verification with user credential verification to provide a more robust authentication mechanism that is convenient to the user and effective across enterprise boundaries. In one implementation, user credential verification and device credential verification are combined to provide a convenient two-factor authentication. In this manner, an account authority service or other authentication provider verify both factors and provide a security token in accordance with the security policy of the account network resource the user is intending to access. The level of privilege granted by the target account network resource can vary depending on the number and type of factors verified by the account authority service.