In OpenResty Edge, you can use a custom ACME certificate issuer (just like Let's Encrypt) to sign a certificate to your domain.
In the global configuration, select "Cert Issuers" from the left sidebar.
Let's create a new certificate issuer here, click the "New Cert Issuer" Button, and then fill the info provided by your certificate issuer.
Once you have created a custom certificate issuer, you can create a certificate, here we create a global certificate for '*.example.com'.
Open the "Global Certificates" page, create a "New Certificate", and the select the issuer you just created, click save.
You can check the log of your certificate issuance, and if you find that the issuance has failed, you can adjust the filled information according to the log information, and then re-issue the certificate.