I develop and support a program which uses (S)FTP to download files to corporate servers. Corporate clients often require my program to go through a proxy rather than connecting directly. Unfortunately, (S)FTP proxies don't seem to be standardized, particularly regarding authentication.
I'd like to find some standard way to interact with an (S)FTP proxy, without knowing the vendor in advance.
If that's not possible, I'd like to pull together a list of the different (S)FTP proxy types, their pros and cons (if I have a choice which to use), how to use them, examples of vendors implementing them, links to more information, etc.