After publishing my vSphere 7 with Kubernetes automation lab deployment script, I was looking at my NSX-T Edge code which leverages the vSphere VM Keystroke API to automate the joining of the the NSX-T Edge to the NSX-T Management Plane. This technique is used to avoid the need for SSH access to both NSX-T Edge and Manager which is the official VMware method as outlined in the documentation for configuring the Edge.
This is certainly unfortunate as most customers normally disable SSH by default and only enable it for troubleshooting/debugging purposes. As far as I know, there are no remote NSX-T APIs for configuring an NSX-T Edge that has been deployed outside of NSX-T Manager, which has its own implications.
I recently had a chance to revisit some research I had made a note of when I had first started working with NSX-T. While inspecting the NSX-T Edge OVA, I found several OVF properties that begin with mp which per the description was referring to the NSX-T Manager. At the time, I was not able to figure out which the required combination of keys and values. Taking a closer look and poking around the appliance and logs, I was able to finally figure out the correct combination which turned out to be easy, once you knew what it was expecting.
To help demonstrate this functionality, I have created a basic PowerCLI script edge-auto-join-nsxt-management-plane.ps1 which uses information from your already deployed NSX-T Manager to automatically deploy the desired number of NSX-T Edge(s) which will automatically join the NSX-T Management Plane upon initial setup.