This is xnu-8019. See this file in:
/* quick and dirty hack to grab all credentials in the cred hash table
 * from kernel via sysctl.
 * sysctl is only defined if xnu is built with DEBUG_CRED defined.
 */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <limits.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <bsm/audit.h>

/* bad!  this is replicated in kern_credential.c.  make sure they stay in sync!
 * Or better yet have commone header file?
 */
struct debug_ucred {
	uint32_t        credp;
	uint32_t        cr_ref;                         /* reference count */
	uid_t           cr_uid;                         /* effective user id */
	uid_t           cr_ruid;                        /* real user id */
	uid_t           cr_svuid;                       /* saved user id */
	u_short         cr_ngroups;                     /* number of groups in advisory list */
	gid_t           cr_groups[NGROUPS];     /* advisory group list */
	gid_t           cr_rgid;                        /* real group id */
	gid_t           cr_svgid;                       /* saved group id */
	uid_t           cr_gmuid;                       /* UID for group membership purposes */
	struct auditinfo_addr cr_audit;                 /* user auditing data */
	uint32_t        cr_label;                       /* MACF label */
	int                     cr_flags;                       /* flags on credential */
};
typedef struct debug_ucred debug_ucred;

void dump_cred_hash_table( debug_ucred * credp, size_t buf_size );
void dump_cred( debug_ucred * credp );


main( int argc, char *argv[] )
{
	int                             err;
	size_t                  len;
	char                        *my_bufferp = NULL;

	/* get size of buffer we will need */
	len = 0;
	err = sysctlbyname( "kern.dump_creds", NULL, &len, NULL, 0 );
	if (err != 0) {
		printf( "sysctl failed  \n" );
		printf( "\terrno %d - \"%s\" \n", errno, strerror( errno ));
		return;
	}

	/* get a buffer for our credentials.  need some spare room since table could have grown */
	my_bufferp = malloc( len );
	if (my_bufferp == NULL) {
		printf( "malloc error %d - \"%s\" \n", errno, strerror( errno ));
		return;
	}
	err = sysctlbyname( "kern.dump_creds", my_bufferp, &len, NULL, 0 );
	if (err != 0) {
		printf( "sysctl 2 failed  \n" );
		printf( "\terrno %d - \"%s\" \n", errno, strerror( errno ));
		return;
	}
	dump_cred_hash_table((debug_ucred *)my_bufferp, len );

	return;
}

void
dump_cred_hash_table( debug_ucred * credp, size_t buf_size )
{
	int             i, my_count = (buf_size / sizeof(debug_ucred));

	printf("\n\t dumping credential hash table - total creds %d \n",
	    my_count);
	for (i = 0; i < my_count; i++) {
		printf("[%02d] ", i);
		dump_cred( credp );
		credp++;
	}
	return;
}

void
dump_cred( debug_ucred * credp )
{
	int             i;
	printf("%p ", credp->credp);
	printf("%lu ", credp->cr_ref);
	printf("%d ", credp->cr_uid);
	printf("%d ", credp->cr_ruid);
	printf("%d ", credp->cr_svuid);
	printf("%d g[", credp->cr_ngroups);
	for (i = 0; i < credp->cr_ngroups; i++) {
		printf("%d", credp->cr_groups[i]);
		if ((i + 1) < credp->cr_ngroups) {
			printf(" ");
		}
	}
	printf("] %d ", credp->cr_rgid);
	printf("%d ", credp->cr_svgid);
	printf("%d ", credp->cr_gmuid);
	printf("a[%d ", credp->cr_audit.ai_auid);
	printf("%d ", credp->cr_audit.ai_mask.am_success);
	printf("%d ", credp->cr_audit.ai_mask.am_failure);
	printf("%d ", credp->cr_audit.ai_termid.at_port);
	printf("%d ", credp->cr_audit.ai_termid.at_addr[0]);
	printf("%d ", credp->cr_audit.ai_asid);
	printf("] ");
	printf("%p ", credp->cr_label);
	printf("0x%08x \n", credp->cr_flags);
	printf("\n");
	return;
}