Function clone_to_temp 

pub async fn clone_to_temp(
    temp_dir: &Path,
    url: &str,
    branch: &str,
    credential: Option<&CredentialKind>,
    follow_redirects: bool,
    mirror: bool,
) -> Result<PathBuf, HttpsCloneError>

Clone url into a new directory under temp_dir and answer it; git creates whatever part of temp_dir is missing.

With no credential the url goes to git as given, so git decides which transports it takes. A mirror also gets an .info.json naming branch and url; when that cannot be written the clone is removed, since the caller never learns where it was.