check_once_cc_set_principal
check_once_cc_set_principal(context, ccache, CC_CRED_MAX, "foo/BAZ@BAR.ORG", CC_ERR_CRED_VERSION, "CC_CRED_MAX (not allowed)");
check_once_cc_set_principal(context, ccache, CC_CRED_V5, NULL, CC_BAD_PARM, "NULL principal");
cc_int32 check_once_cc_set_principal(apiCB *context, ccache_p *ccache, cc_int32 cred_vers, const char *in_principal, cc_int32 expected_err, const char *description);