Do we have a list of available environment variables listed anywhere? I have looked through the documentation, but so far am unable to locate a comprehensive list.
Nothing on the website today, but you can grep through the source code for Envar - should be pretty self-explanatory:
Thanks for this suggestion, it occurred to me also sometime after posting my question.
I have reviewed the search link you provided - In truth I was expecting a repo password environment variable, but from what I can see no option exists.
KOPIA_PASSWORD is what you’re looking for.
I must have missed that when reviewing the link, sincere apologies.
Many thanks for your support, as always! 
Edit: Searching Getenv seems to yield additional results.