A server may want to specify a callback routine so that it knows when a context gets first used. This user-defined callback may be specified through the rpc_gss_set_callback() routine. The callback routine is invoked the first time a context is used for data exchanges, after the context is established for the specified program and version.

The user-defined callback routine should take the following form:

bool_t callback(struct svc_req *req, gss_cred_id_t deleg,
     gss_ctx_id_t gss_context, rpc_gss_lock_t *lock, void **cookie);

rpc_gss_set_callback() takes one argument: a pointer to a rpc_gss_callback_t structure. This structure contains the RPC program and version number as well as a pointer to a user-defined callback() routine. (For a description of rpc_gss_callback_t and other RPCSEC_GSS data types, see the rpcsec_gss(3NSL) man page.)

The user-defined callback() routine itself takes the following arguments:

req

Pointer to the received service request. svc_req is an RPC structure containing information on the context of an RPC invocation, such as program, version, and transport information.

deleg

Delegated credentials, if any. (See NOTES, below.)

gss_context

GSS context (allows server to do GSS operations on the context to test for acceptance criteria). See NOTES, below.

lock

This parameter is used to enforce a particular QOP and service for a session. This parameter points to a RPCSEC_GSS rpc_gss_lock_t structure. When the callback is invoked, the rpc_gss_lock_t.locked field is set to TRUE, thus locking the context. A locked context will reject all requests having different values for QOP or service than those specified by the raw_cred field of the rpc_gss_lock_t structure.

cookie

A four-byte quantity that an application may use in any manner it wants to -- RPC does not interpret it. (For example, the cookie could be a pointer or index to a structure that represents a context initiator.) The cookie is returned, along with the caller's credentials, with each invocation of rpc_gss_getcred().

rpc_gss_set_callback() returns TRUE if the use of the context is accepted; false otherwise.

See attributes(5) for descriptions of the following attributes:

rpc(3NSL), rpc_gss_getcred(3NSL), rpcsec_gss(3NSL), attributes(5)

ONC+ Developer's Guide

Linn, J. RFC 2078, Generic Security Service Application Program Interface, Version 2. Network Working Group. January 1997.

If a server does not specify a callback, all incoming contexts will be accepted.

Because the GSS-API is not currently exposed, the deleg and gss_context arguments are mentioned for informational purposes only, and the user-defined callback function may choose to do nothing with them.