Return True if role is whitelisted or roles cannot be determined.

def _is_whitelisted(self, req):
        """Return True if role is whitelisted or roles cannot be determined."""

        if not self.roles_whitelist:
            return False

        if not hasattr(req, 'context'):
            self.log.info("No context found.")
            return False

        if not hasattr(req.context, 'roles'):
            self.log.info("No roles found in context")
            return False

        roles = req.context.roles
        self.log.debug("Received request from user with roles: %s",
                       ' '.join(roles))
        for key in self.roles_whitelist:
            if key in roles:
                self.log.debug("User role (%s) is whitelisted.", key)
                return True

        return False