http://dlang.org/phobos/std_digest_sha.html#SHA1
Not quite the same, the oauth requires hmac.When I did this in my oauth.d for twitter and stuff, I used the C library "mhash"
check out my code: https://github.com/adamdruppe/arsd/blob/master/oauth.d#L796The rest of that lib is kinda sloppy and has a few dependencies from my other modules but feel free to use whatever looks useful to you.
I think mhash is GPL licensed.