opencascade-6.8.0.tgz is available from http://files.opencascade.com/OCCT/OCC_6.8.0_release/opencascade-6.8.0.tgz which does not require login and can be fetched by portage. Please consider using this as SRC_URI and removing RESTRICT="fetch" in order to ease automated installation.
I think SRC_URI="http://files.opencascade.com/OCCT/OCC_${PV}_release/opencascade-${PV}.tgz" is correct in 6.8.0-r1, right? commit 5c5a29323b20138103ace226b0048059d792b779 (HEAD -> master, origin/master, origin/HEAD) Author: Michael Weber <xmw@gentoo.org> Date: Mon Jun 5 00:51:52 2017 +0200 sci-libs/opencascade: Remove RESTRICT=fetch (bug 619300, bug 600514). Package-Manager: Portage-2.3.6, Repoman-2.3.2 sci-libs/opencascade/opencascade-6.7.1-r1.ebuild sci-libs/opencascade/opencascade-6.8.0-r1.ebuild sci-libs/opencascade/opencascade-6.9.0-r1.ebuild sci-libs/opencascade/opencascade-6.9.1-r1.ebuild