There are a lot of options available for selecting SSL certificates to secure your website. Many Certificates uploaded to StackPath will have to specifically cover all subdomains you wish to add as your delivery domain. To get around having to upload a new certificate for every delivery domain change, we recommend a special kind of certificate, called a wildcard certificate to cover your website.
What is a Wildcard Certificate?
Wildcard certificates are unique because they can be used to cover any subdomain attached to the root domain that is covered by the certificate. This is usually represented by a '*' in place of any subdomain covered by the certificate. When searched on https://www.sslshopper.com/ the certificate will indicate that coverage includes *.yourdomain.com.
Using a Custom Subdomain
With a wildcard SSL certificate, you can use any custom subdomain as a Delivery Domain, you will just have to add it to the Delivery Domain section, and create a CNAME record to point that subdomain to the Edge Address.
For example, cdn.yourdomain.com can be used as the delivery domain for static content integration, with the CDN subdomain pointed to the Edge Address as a CNAME record. With HTTP/2 delivery enabled from both your website and from StackPath CDN, and a wildcard SSL certificate, this is the ideal solution for a custom delivery domain.
Using Custom Subdomains for Domain Sharding
Parallelize Downloads is a common optimization suggestion in many speed tests that can be achieved by adding more subdomains with a method known as domain sharding. This is the practice of pulling content from multiple subdomains to allow for faster transit since there will be more concurrent connections. The wildcard SSL certificate comes in handy for this because it will allow you to cover any number of these subdomains, meaning cdn.yourdomain.com, cdn2.yourdomain.com, cdn3.yourdomain.com, and so on will all be covered by your certificate.
This is only recommended if your webserver does not support HTTP/2 encoding. HTTP/2 alleviates the need for domain sharding, so you will only need one custom delivery subdomain.