Which server-role does the system has?
You can set the values manually without doing a certificate check but make sure nobody is attacking you currently via a MITM attack:
eval "$(ucr shell)"
ucr set umc/saml/idp-server="https://ucs-sso.$domainname/simplesamlphp/saml2/idp/metadata.php"
wget -O "/usr/share/univention-management-console/saml/idp/ucs-sso.$domainname.xml" --no-check-certificate "https://ucs-sso.$domainname/simplesamlphp/saml2/idp/metadata.php"
ucr commit /etc/pam.d/univention-management-console
ucr commit /etc/ldap/sasl2/slapd.conf
univention-run-join-scripts