You don't need this.
There is only 1 URL for your ADFS farm and as soon as you want external clients to connect to it, it has to be a public name. So you get a cert for adfs.domainA.com or with a SAN for that namespace (that can also be a wildcard SAN), then you create a split
brain DNS in your environment to make sure that your internal clients resolve adfs.domainA.com to the local IP address of your ADFS farm and you configure your external DNS to have external client resolving the same name to the public IP address of your WAP
server farms (ADFS proxies).
This is listed here under network requirements section:
https://docs.microsoft.com/en-us/windows-server/identity/ad-fs/overview/ad-fs-requirements
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