cc_ccache_set_principal
err = cc_ccache_set_principal(ccache, cc_credentials_v5, "foo@BAR.ORG");
#ifndef cc_ccache_set_principal
#ifdef cc_ccache_set_principal
err = cc_ccache_set_principal(ccache, cred_vers, in_principal);
err = cc_ccache_set_principal(ccache, cc_credentials_v5, "foo@BAR.ORG");