Preferred way to recurse over a directory?

[Albert Brox <albert@xxxxxxxxxxx>]

I'm working on PR #20239 loadcred-dir and wondering what the preferred 
way to recurse over a directory is.

I was told recursively calling the `load_credential` function is too 
racy so I'm led to ftw/nftw. However I see in the TODO file, "Get rid of 
nftw(). We should refuse to use such useless APIs on principle." Can 
anyone point me in the right direction?

Best
Albert