A computer in an untrusted cloud network functions as a cloud-based enterprise application store via which a client computer (client) establishes a connection to an enterprise application in a trusted enterprise network. User authentications are performed in both a login phase and subsequent application launch phase, each authentication receiving from the client and transmitting to the enterprise network an encrypted password and encrypted key, the encrypted password being a user password encrypted under a first one-use symmetric key, the encrypted key being the first symmetric key encrypted under a public key of a private/public key pair of the enterprise network. The enterprise network decrypts the encrypted key and encrypted password to obtain the user password for authenticating the user. The launch-phase authentication includes use of a login ticket including a second one-use symmetric key under which the user password is encrypted and stored in encrypted form in the enterprise network.