I think it's good advice to not pass secrets through environment variables. Env vars leak a lot. Think php_info, Sentry, java vm dumps, etc. Also, env vars leak into sub-processes if you don't pay extra attention. Instead, read secrets from a vault or from a file-system from _inside_ your process. See also [1] (or [2] which discusses [1]). Dotnet does this pretty good with user secrets [3].
[1] https://blog.diogomonica.com/2017/03/27/why-you-shouldnt-use... [2] https://security.stackexchange.com/questions/197784/is-it-un... [3] https://learn.microsoft.com/en-us/aspnet/core/security/app-s...