This is for administrators at SUNET TCS members for the 2020- "Sectigo generation" of the SUNET TCS service.
If you are a user of SUNET TCS but not an administrator, please see SUNET TCS documentation at your organization.
Our SUNET instance of SCM
Our SUNET instance of the Sectigo Certificate Manager is at https://cert-manager.com/customer/sunet
To access it, you need to have your organization and your admin user(s) set up. See below under "Getting access to the system".
Help from SUNET TCS
Email firstname.lastname@example.org after making sure that this document does not contain the answer to your question or a solution to your problem.
Help from Sectigo Support
If instructed by SUNET TCS or this document, contact Sectigo Support using https://sectigo.com/support-ticket with your support question/problem. Unless instructed otherwise, select "SCM Validation" as the reason for the ticket if it relates to validation problems, or "SCM Support" for other issues. In the description, include a line saying "We are a SUNET member of the GEANT TCS service, using the https://cert-manager.com/customer/sunet SCM instance."
Sectigo documentation can be found at https://support.sectigo.com/Com_KnowledgeProductPage?c=Sectigo_Certificate_Manager_SCM
- "SCM - Sectigo® Certificate Manager Quick Start Guide" is a short introduction to the SCM system
- "SCM - Sectigo Certificate Manager Administrator's Guide" is the very much longer description
- "SCM - Sectigo Certificate Manager REST API" describes the REST API
Differences from the DigiCert generation 2015-2020
New vendor, new web interface
Sectigo is the new vendor for TCS instead of DigiCert. We are using their Sectigo Certificate Manager (SCM) instead of DigiCert CertCentral. The rest of this section describes the most important changes you need to understand.
No "division" objects in the new system
There is no concept of divisions in SCM as there was in DigiCert CertCentral.
- SUNET TCS has an instance of SCM at https://cert-manager.com/customer/sunet which is used by all SUNET TCS administrators (at your level and at the SUNET "superuser" level) but not by GEANT TCS members from other countries.
- At the SUNET level, we cannot just create a division for a SUNET TCS member and ask you to create an organization object yourselves with all relevant information, as you did in CertCentral. We have to create an Organization in the system to be able to add you. See below for more practical information on how you join.
- If you need to validate another organization (due to the need to have something different in the O= field of the certificates), that new organization will be "at the same level" as your original organization and there is no division that contains them. You will have acess to both organization due to the fact that we/you will add the same admins for both organizations.
No "User level users"
In DigiCert CertCentral, there were two basic kind of users: "Administrators", who could order/approve certificates, change settings and do other admin level stuff, and "Users" who could only request certificates (but who were nevertheless authenticated by logging into CertCentral just like the Administrators).
In the SCM, there are basically only Administrator level users. In fact, the SCM does not talk about users, it talks about admins. That means that you cannot have users logging in to the SCM who can only request certificates. See below under "SSL certificates" for solutions to this.
The SCM lets you create Departments under Organizations. Just like the Organization name is what goes into the O= of a certificate, the Department name is what goes into the OU= of a certificate. You can use Departments in two ways:
- Just as a tool to sort certificates and get the correct OU= set, but it will still be the Organization's admins doing the approval.
- To delegate approval of certificates to department admins for their department. In most(?) cases that would be combined with registering a subdomain (or a completely different domain) and restrict the department to that.
MRAO, RAO, DRAO!
There are three levels of admins in the SCM, all called something with RAO (Registration Authority Officer) in the name:
- MRAO: the "superuser level" for SUNET people that can work with all organizations, departments, domain, certificates, admins, etc.
- RAO: the admin level for working with an organization and the departments, domains, certificates, admins etc that belong to that organization.
- DRAO: the admin level for working with a department, and the domains, certificates, admins etc that belong to that department.
It is a bit more complicated than that: a RAO is connected to one or more organizations, and a DRAO to one or more departments, and there is also the possibility to only have the right for SSL certificates, client certificates and/or code signing certificates. Thus, an admin could be "RAO - SSL Certificates" and "RAO - client certificates" for Organization A, while also being "DRAO - SSL Certificates" for a department belonging to another organization.
The first admin you will get when joining with your organization will be RAO for all certificate types and for your organization.
Getting access to the system
Members of the "Digicert generation" 2015-2020 service
To get access to the new system, email email@example.com with a subject line like "TCS2020: organization name" and tell us:
- First name, last name, email and preferred user name for the first admin (RAO) of your organization. That person should be a current Administrator in the DigiCert CertCentral system.
- Organization name, adress line, postal code, city and county (län).
We know that Sectigo uses at least https://www.infobel.com/en/sweden and https://proff.se/ to check address and postal code, so please try to find a record there for your organization and use that address line and postal code if it is not obviously wrong (it's not likely that people will rely on the address information in your OV certificates to send you paper mail...). Also, they seem to prefer the visiting address (besöksadress) over the mailing adress (postadress) so please use the former.
If you try to use other address/postal code information you risk having your organization validation delayed. You are encouraged to include a direct link to the matching infobel/proff record in your email.
New members (not in the "DigiCert generation" 2015-2022 service)
If you have not been a member of the 2015-2020 "DigiCert generation" of the service, you are still welcome to join. SUNET TCS is available to all SUNET customers without extra charge. Contact firstname.lastname@example.org about membership in the service. Do not send any paper documents before that.
Please note that during the spring of 2020 we are prioritizing bringing the current members over to the new service.
You must validate one or more domains before you can have certificates issued. There are multiple steps in this process. This is how you add the doman example.org:
- Make sure that you are not having CAA records in your DNS zone that forbids Sectigo from issuing certificates for the domain. If that is the case, domain validation will fail too. Having no CAA records is OK, as is having CAA records mentioning "sectigo.com" as approved.
- Go to Settings → Domains → Delegations and press the Add button. Fill in the domain name (example.org) and the optional description. Select the type of certificates (SSL, client, CS) that should be enabled for this domain. For your main domain you would typically enable all of them, but for most additional domains you would only enable SSL certificates. If you have set up Departments and this domain should be delegated to the DRAOs of that department, expand the selection line and enable the domain for the right department and the appropriate types too.
- Use Add again, embrace the cargo cult, and redo exactly the same step for the domain name with "*." prepended to it (*.example.org in our example).
- Wait for a SUNET MRAO to approve your domain delegations. Unfortunately, this step is necessary at this time, but we have asked Sectigo to remove it. When this is done, the delegation status will be Approved and you can proceed to the next step.
- Switch from the Delegations to the DCV tab. Click on the the right line to check it, and use the DCV button that appears to initiate DCV. Select method:
- Email means that your select one of the five allowed addresses for the domain, and then receive and handle an email sent to that address. For our example, it would be one of "email@example.com", "firstname.lastname@example.org", "email@example.com", "firstname.lastname@example.org" or "email@example.com".
- CNAME means that you will be instructed to put a CNAME record with a hash value name in your DNS zone, pointing to another hash value. The system will tell you the values. Please verify using an external resolver that the CNAME record is in place and externally visible.
- HTTP/HTTPS means that you will be instructed to put certain contents in a file with a certain name on the web server for your domain name.
- Follow the instructions for the method you selected.
- When the validation is OK, you will see Validation Status as Validated in the DCV tab. In the Delegations tab, the domain itself should also be shown as Validated. The extra record with "*." prepended will still show as Not Validated for some time (hours to a day) and will then be updated to be Validated too.
- You are now ready to use this domain and its subdomains for certificate requests. You do not have to wait for the "*"-prepended domain to be shown as Validated.
If you need additional organization names (values for the O= part of a certificate), that will have to be added by a SUNET MRAO for you. Follow the same steps as for your first organization (see above under "Getting access to the system"), but instead of providing information about a "first admin", tell us the usernames for the administrators of your "main organization" that should also be RAOs for the new organization.
Note: you will not add an extra organization ("Smorgasboda Hogskola" in addition to "Smörgåsboda Högskola") for a name without non-ASCII characters for grid certificates, as that will be handled differently. We will update this document when Sectigo has provided the details.
To add a department:
- Go to Settings → Organizations and click on the organization line to check it, then use the Departments button to bring up the listing window and press Add.
- Fill in the desired OU= name component in the Department Name field. The rest of the name components will be as for your organization.
- Select the Client Certificate tab and disable Key Recovery for MRAO and DRAO ("Allow Key Recovery by Master Administrators" and "Allow Key Recovery by Department Administrators", respectively). It will already be disabled for RAOs as that was part of the organization setup done by SUNET.
- Do not fret over other options on the various tabs, as they can be changed later. Do not enable or change things you do not understand. Finish using the OK button.
Admins connected to the department
You can now go on to create admins (see below) that are DRAOs connected to just this department instead of being RAOs for the whole organization.
Domains connected to the department
If you add department admins (DRAOs) that can approve certificates for their department, you will most likely want to limit them to their own domain (department-example.com) or a subdomain of your main domain (department.example.org) if we imagine that your main domain is example.org.
In the first case with a completely new domain for the department, follow the normal domain validation procedure above to add department-example.com and *.department-example.com with delegation to the department and initiate DCV as you did for your main domain.
In the second case with a subdomain of your already validated main domain, you will still add department.example.org and *.departement.example.org with delegation to the department but you will not have to initiate DCV again, as the SCM is smart enough to know that example.org is already validated. As for your main domain, you should expect department.example.org to show as Validated at once, and *.department.example.org with some delay.
You create additional admins (RAOs for your whole organization or DRAOs for departments you have created) under the Admins tab with the Add button. You can also edit existing admins by clicking on the line to check them and then using the Edit button.
- Fill in login (with a suitable user name), email, forename and surname. We advice you to leave the rest of the contact information empty, as it is not needed.
- Select "Your institution" as Identity Provider and fill in the admin's ePPN ("SWAMID identity") in IdP Person Id to enable the admin to login via SWAMID when SAML has been set up correctly.
- A password has to be provided for a new admin. The first time they login they will have to change it.
- Select the desired privileges under Privileges. Do not check "WS API Use Only" (will be explained later).
- Select the desired roles under Roles which means selecting the right combinations of level (RAO for your organization or DRAO for a department you have created) and certificate type (SSL, client or code signing).
- When done, you have to communicate the selected password to the new admin (it is not emailed by the system).
We strongly recommend that you create personal admin users (not shared ones), to be able to see who has done what in the system.
It has been reported that some privileges (management of peer admins, Allow DCV) cannot be assigned by one RAO to another. If that affects your organization email firstname.lastname@example.org to have it fixed manually. Tell us the usernames involved and what privileges you want to add. We'd like that email to come from an admin that already has "Allow creating/editing of peer admin users" instead of the admin who wants more privileges.
You can get locked if you fail to login a number of times. You will then get an "Incorrect login details, account is locked, password has expired or your source IP is blocked." message when you try to login, even if you use the correct password. It will be the case even if your password have been changed by another admin who can do that for you. This requires the lock to be reset and that can only be done by an MRAO, so you need to contact email@example.com.
Applying for and approving certificates in the SCM as an admin
Go to Certificates → SSL Certificates and press Add to request a certificate.
- Select the Manual creation of CSR mode
- Provide a CSR by pasting it into the text area or upload it as a file using the Upload CSR button.
- Select and fill in the right information in the Basic info step. Make sure you select a multi-domain certificate type to get a text box to fill in Subject Alternative Names if needed. If you request this on behalf of somebody else, you can add their email address as External Requester.
- You can use "Click here for advanced options" to get access to a comment field where you can enter information you want to be able to see later. Do not remove address fields using the Remove checkboxes as that seems to cause the certificate to be stalled as the information will not match the pre-validated organization information.
- On the next screen, accept or decline auto-renewal and finish with OK.
If your admin has the "Allow SSL auto approve" privilege selected, the certificate will be automatically approved (which makes sense, because why would you have entered all the information above if you did not want to approve the certificate?) and will show up as "Applied".
If your admin does not have that privilege selected, the certificate will show up as "Requested" and you will have to approve it by selecting it and using the Approve button.
When the certificate has been issued, its status will be shown as "Issued" and you will get an email about it.
If needed, you can also download the certificate by clicking on the line to check it and using the Details button, then the Select button to the right of "Download The Certificate".
Notes on specific certificate types
GÉANT OV SSL
Currently (2020-04-08), if you use the GÉANT OV SSL type and request a certificate for
mail.test.example.org, you will get that name put in a DNS Subject Alternative Name, but you will also get a DNS Subject Alternative Name for www.mail.test.example.org . We recommend that you use GÉANT OV Multi-Domain instead if you do not want this, as no extra www-prepended name is added for that type. This has been reported to GÉANT.
If you need EV certificates, talk to firstname.lastname@example.org about how to proceed before you do anything at all in the SCM, as the procedure will not be to just to request an individual EV certificate, and you may be locked out of ordering normal OV certificates while EV validation takes place. Also, we would very much like to work with you to document the process, so we can document it here for the benefit of other members.
IGTF (Grid) Certificates
We are waiting for the grid certificate profiles to be correct before advising you about them.
Allowing non-admins to request certificates
You can allow persons who are not admins in the SCM to request certificates ("enroll" in Sectigo-speak). To do that, go to Settings → Organizations and select your organization and select Edit. (Or, if this should apply only to a departement, after selecting the organization, use the Departments button, select the department, and use Edit on that instead).
- On the SSL Certificate tab, enable Self Enrollment and put a shared secret value in Access Code and copy the URL present below that field. You can now hand out this URL to persons who can use it with the access code to access the Certificate enrollment page for non-admins. As you can see when you test using it, it contains approximately the same fields as the "Add Certificate" pages in the SCM itself. Be aware that the email address is not checked (more than for having the right domain) so you need an out-of-band method of authenticating the requestor.
- If you have SAML attribute release working towards Sectigo (see "SAML Configuration" below), you can also enable "Self Enrollment via SAML", keep the Access Code secret and hand out the URL below the Token field to users. They will then have to authenticate using SAML before getting to the same kind of enrollment form as above. As the email address will now come from your IdP via SAML you can be more confident that it is correct, but it is up to you to decide if it is good enough, or you still will require additional conformation out-of-band before approving.
- Do not enable "Automatically Approve Self Enrollment Requests". At least, you will want to manually approve certificate requests arriving via this route!
- While you are at it, you will want to Customize the Server Software so the users are not presented with a gazillion choices. Also, you might also want to customize the SSL Types for the Enrollment Form (on the right-hand side), to stop users from selecting certificate types you do not want them to. You can still keep the ability to select them in the SCM (the left-hand Admin UI selection).
Self-service portal via SAML
Configuring your IdP and the SCM to enable the portal
The self-service portal is located at https://cert-manager.com/customer/sunet/idp/clientgeant
For it to work for your users, you need to
- Have your IdP configured correctly for Sectigo. See below under "SAML Configuration".
- Edit your organization object and set "Academic code (SCHAC Home Organization)" to the same value as your IdP sends for schacHomeOrganization. It will typically be your main domain, but confirm this with your IdP admins.
For it to work for your users who need IGTF/grid certificates, you also need to:
- Edit your organization object and set "Secondary Organization Name" to the name used in grid certificates (with åäö transcribed correctly to ASCII if needed, and with the same upper/lowercase conventions that you have used before with DigiCert). Please check existing certificates if you are unsure or as a last resort, ask us at SUNET TCS to help you check. As grid certificate subjects are used as "usernames" in systems, it is vital that the whole subject string is kept as it was before for your users.
- Email email@example.com about this so that we can ask for a validation of the secondary name as you cannot perform this step yourself.
Configuring your relying servers (for grid/IGTF)
For the "normal" client certificates, you should not need to configure anything.
For the grid/IGTF certificates, make sure that your servers have an up-to-date IGTF Trust Anchor Distribution that includes trust for "
/C=NL/O=GEANT Vereniging/CN=GEANT eScience Personal CA 4" (for example found in the
ca_GEANTeSciencePersonalCA4-1.105-1.noarch.rpm or newer RPM package)
Using the portal
The instructions here are geared towards certificate-aware RAOs. You may need to expand on this when providing instructions for your end users, for example by showing them where to import certificates in your supported web browsers, etc.
This is how you get a certificate:
- Go to https://cert-manager.com/customer/sunet/idp/clientgeant, select your organization's IdP and login there.
- Select the right certificate profile:
- Use "GÉANT Personal Certificate" for normal client certificate for email signing etc outside of the grid/IGTF world.
- Use "GÉANT IGTF-MICS Personal" for a grid/IGTF personal (client) certificate for normal use
- Use "GÉANT IGTF-MICS-Robot Personal" for a grid/IGTD robot personal certificate (seldom used)
- Select if you want the key generated on the server side or locally. While the former is more convenient, there may be policy reasons or technical reasons for not using that:
- Use "Generate RSA" if you want a certificate with the key generated on the server side.
- Use "Generate ECC" only if you are testing ECC certificates. If unsure, use RSA.
- Use "Upload CSR" and choose the CSR file you have generated if you do not want the key generated on the server side.
- If you choose to upload the CSR, you must first have created your key and CSR locally, using whatever software you use for that. With OpenSSL, that could be:
openssl req -new -newkey rsa:2048 -out usercert_request.pem -keyout userkey.pem -subj '/CN=Mitt Namn' chmod go= userkey.pem cat usercert_request.pem
- If you choose to generate the certificate on the server side, you must provide the password used to encrypt the PKCS#12 file that will be generated.
- Click "Submit" and accept the click-through license.
- After a short while, you will get to dowload your certificate. The format depends on your choice above:
- With "Generate RSA/ECC", you will get a PKCS#12 file called certs.p12 containing key and certificate. You can import that in your browser using "Import Certificate" or similar.
- With "Upload CSR", you will get a PEM-formatted certs.pem containing just the certificate. If you need it in your web browser, you need to create a PKCS#12 file yourself. With OpenSSL as above, that could be:
openssl pkcs12 -export -inkey userkey.pem -in certs.pem -out certs.p12
- If you get the error message "Sectigo Certificate Manager enrollment request failed. Please contact your security administrator." when you have clicked the submit button and accepted the click-through license, it may be because you have hit the limit of two valid certificates per identity and certificate profile. You need to revoke at least one of the two certificate before another one can be issued. 2020-04-27: This behaviour will be reported as a bug to Sectigo to ask them to handle this in a smoother way.
Revoking client certificates
End users cannot revoke certificates themselves in the self-service portal. Instruct them to contact you if revocation is needed. You as RAOs can revoke certificates by going to Certificates → Client Certificates, selecting the right person, clicking Certificates, selecting the right certificate and clicking Revoke.
Issuing client certificates using the SCM
Note: this is a backup solution. The main way to issue client certificates is via the self-service portal discussed above. With that understood, this is how you can issue personal certificates using the SCM:
- As a RAO, go to Certificates → Client Certificates and use the Add button. Select the appropriate Organization, Department and Domain. Fill in the Email Address and the Common Name. Fill in the separate name fields. Leave Secret ID blank and Validation Type Standard.
- You have now added the person, rather than a certificate. Click the person to check the line and use the Certificates button. There, use Send invitation to send an invitation email to the user, containing a nonce that authorized that user to create a client certificate.
- The user will have to provide a Password (that will be used to encrypt the generated PKCS#12 file) and a Passphrase (that can be used to revoke the certificate without your assistance), as well as accept a click-through license.
- The user will then receive a PKCS#12 file containing the key, certificate and chain ready for importing in web browsers etc.
Things worth noting:
- Yes, the key is always generated on the server side when you use this method. There is no option of uploading a CSR to keep use a key generated on the client side. This may not be acceptable for users due to policy (not allowed to have the key generated on the server side) or technical reasons (key not exportable from hardware device). You can upload a CSR when you use the self-service portal.
- There is also the option of enabling a AccessCode, which is a shared secret between you and all users than enable them to get a client certificate as long as they have access to their email. We advise you not to use that.
- There is also the possibility to enter a SecretID per user, to enable them to get a client certificate by entering that together with their email address. For occasional client certificates, we do not see the upside of this as compared to the invitation method above, and for bulk issuing we will rely on the self-service portal via SAML as soon as that is ready.
Code Signing Certificates
We will update this section when a SUNET TCS member has found the need for a code signing certificate, gone through the procedure and shared the experience with us.
Under Settings → Notifications you can add and edit what notifications the system will send you when certain conditions are met. Use the Add button to have a look at the various Notification Types that are available.
- You should add at least a notification for SSL Expiration to make sure you get expiration emails matching the ones you got from the earlier systems. Also DCV Expiration should be added for the same reason.
- If you have made it possible for non-admins to request certificates (see above), you may also want to get SSL Awaiting Approval to be aware that there is a request to approve.
- Please do not enable "Notify MRAO Admin(s)" as that would send email to the SUNET level "superusers" too.
If you have a need to change the text in the emails sent from the system, you can do that under Settings → Templates → Email Template. If you do, please report your experience with that feature (good or bad) to firstname.lastname@example.org.
Configure your IdP to work with Sectigo
SAML login is activated for the SUNET instance of SCM but you need configure the attribute manually in your Identity Provider due to that the SCM entity in metadata has no defined entity category. The reason behind this is that Sectigo has registered their Service Provider in inCommon and they can't issue the European only entity category .GÉANT Data Protection Code of Conduct.
The following single valued attributes should be released to the entityId https://cert-manager.com/shibboleth:
- eduPersonPrincipalName (urn:oid:220.127.116.11.4.1.5918.104.22.168.6)
- mail (urn:oid:0.9.2342.19200300.100.1.3)
- displayName (urn:oid:2.16.840.1.113722.214.171.124)
- givenName (urn:oid:126.96.36.199)
- sn (urn:oid:188.8.131.52)
- schacHomeOrganization (urn:oid:184.108.40.206.4.1.25220.127.116.11)
eduPersonEntitlement (urn:oid:18.104.22.168.4.1.5922.214.171.124.7) with the value urn:mace:terena.org:tcs:personal-user
Please note that this entitlement value must only be released for those users that fulfils the requirements for requesting personal certificates, within Sweden the requirement is SWAMID Assurance Level 2 Profile (SWAMID AL2), or higher.
SWAMID has added instruction for both Shibboleth IdP and ADFS at the page Konfigur SAML-konfiguration Sunet TCS.
Test that your IdP is correctly configured
After your Identity Provider administrators has configured the attribute release you should test it at https://cert-manager.com/customer/sunet/ssocheck. In this test only eduPersonPrincipalName and mail is required but for the upcoming personal certificates givenName, sn, displayName, schacHomeOrganization and eduPersonEntitlement (not displayed in the test right now) will be required. To further dig down and test you can look at https://cert-manager.com/Shibboleth.sso/Session after a login to see what attributes was released from your Identity Provider and recognised by Sectigo.
When you have verified that your IdP is correctly configured, you can go on to configure use of SAML authentication:
- To use federated login in the SCM portal you need to go into all your current RAO and DRAO admin accounts (Admins) and change the field Identity provider to "Your institution" and the field IdP Person Id to the ePPN (eduPersonPrincipalName) of the admin. If you don't do this manual mapping of eduPersonPrincipalName to the admin account then a much more insecure automatic mapping by mail address will be done at first SAML login. Right now there is a annoying known bug when using the SAML integration. The SAML integration picks up the name from the SAML assertion but don't handle character encoding correct.
- See above under "Allowing non-admins to request certificates" for information about "Self Enrollment via SAML" for SSL certificates.
Using the REST API
Sectigo REST API documentation can be found at https://support.sectigo.com/Com_KnowledgeProductPage?c=Sectigo_Certificate_Manager_SCM in the "SCM - Sectigo Certificate Manager REST API" document.
Authentication is via login name and password for a RAO or DRAO admin. The
customerUri is "sunet".
We recommend that your create separate RAO or DRAO admins to use with the API instead of reusing the same admins as for web UI work. To create an API-only admin:
- Use your RAO to create the new admin as you would create a "normal web UI admin", including setting a temporary password. You will not be able to use the API with this temporary password.
- Login to the new admin in the SCM and perform the mandatory initial password change for it.
- Back with your original RAO, edit the new admin and set the "WS API use only" flag for it.
More gotchas we have discovered, so you do not have to discover them too:
- To be allowed to use the API calls for handling certificates, you must edit the appropriate Organization or Department object, and on the SSL Certificate tab, enable the Web API checkbox. You will be required to provide a value for the Secret Key field too. Enter a good random value there and promptly forget it (it is not used for the current REST API but for an older SOAP API).
- Be aware that the
"serverType": -1in their certificate enroll example refers to the "other" Server Software type, so if you have removed that when cleaning up useless Server Software types, that example will not work.
As inspiration for API use, Fredrik Domeij at UmU has provided bash scripts to request and retrieve certificates. You find them as umu-example-api-bash.tar.
There is support for ACME and some of the test members have started to try that. We will update this section as we get feedback.
What about the expiring certificates in the certificate chain?
Some of you may have noticed that the chain certificates we get from Sectigo contains a certificate at the top with
CN = AddTrust External CA Root and an expiration on 2020-05-30. For an explanation of why this should not cause problems for you, please see "Sectigo AddTrust External CA Root Expiring May 30, 2020" on the Sectigo site.
You may also notice that the next level down in the chain is
CN = USERTrust RSA Certification Authority which also expires on 2020-05-30, and that is the certificate that has signed the
CN = GEANT OV RSA CA 4 certificate that in turn has signed the SSL certificate for your server. That also seems bad, doesn't it? It turns out that certificate is there to support the CN = AddTrust External CA Root "feature" and that there is another version of
CN = AddTrust External CA Root present in the root store of the browsers (using the same key) which is valid until 2038-01-18, and that is the one that matters and makes the browser trust the GEANT-branded CA certificate and therefore your server certificate.
The conclusion is that things will work after 2020-05-30 too.
Do we really need all those certificates in the chain?
No. You should be fine with only the GEANT-branded sub-CA certificate (CN = GEANT OV RSA CA 4 or similar) configured as chain certificate in your server.
Where can we check if our server sends the correct chain?
We recommend Qualys SSL Server Test which tests this and and a lot of other useful things (most of them related to you server configuration, not the certificates as such). For the chain specifically, look at the "Chain issues" heading where you want to see "None" (if you have trimmed the unnecessary certificates from the chain) or "Contains anchor" (if you have kept the full set).