The client may wish to identify itself, for example, as it is identified on a UNIX(tm) system. The flavor of the client credential is "AUTH_SYS". The opaque data constituting the credential encodes the following structure:
struct authsys_parms {
unsigned int stamp;
string machinename<255>;
unsigned int uid;
unsigned int gid;
unsigned int gids<16>;
};
The "stamp" is an arbitrary ID which the caller machine may generate. The "machinename" is the name of the caller's machine (like "krypton"). The "uid" is the caller's effective user ID. The "gid" is the caller's effective group ID. The "gids" is a counted array of groups which contain the caller as a member. The verifier accompanying the credential should have "AUTH_NONE" flavor value (defined above). Note this credential is only unique within a particular domain of machine names, uids, and gids.
The flavor value of the verifier received in the reply message from the server may be "AUTH_NONE" or "AUTH_SHORT". In the case of "AUTH_SHORT", the bytes of the reply verifier's string encode an opaque structure. This new opaque structure may now be passed to the server instead of the original "AUTH_SYS" flavor credential. The server may keep a cache which maps shorthand opaque structures (passed back by way of an "AUTH_SHORT" style reply verifier) to the original credentials of the caller. The caller can save network bandwidth and server cpu cycles by using the shorthand credential.
The server may flush the shorthand opaque structure at any time. If this happens, the remote procedure call message will be rejected due to an authentication error. The reason for the failure will be "AUTH_REJECTEDCRED". At this point, the client may wish to try the original "AUTH_SYS" style of credential.
It should be noted that use of this flavor of authentication does not guarantee any security for the users or providers of a service, in itself. The authentication provided by this scheme can be considered legitimate only when applications using this scheme and the network can be secured externally, and privileged transport addresses are used for the communicating end-points (an example of this is the use of privileged TCP/UDP ports in Unix systems - note that not all systems enforce privileged transport address mechanisms).