The OpenPGP specification (RFC 4880) describes, [page 34][1], the different capabilities that an OpenPGP key may have; including:

> 0x20 - This key may be used for authentication.

In [GnuPG][2], one of the most popular implementations of OpenPGP, it is possible to generate [sub]keys with the authenticate capability (using the `--expert` flag). Okay, great, I know have a key which has the four capabilities – Encrypt, Certify, Sign, Authenticate (ECSA). Now what?

I am curious about that Authenticate capability. **Is there any real-world use for authentication OpenPGP [sub]keys**, other than [not using them and export them as SSH keys][3] instead?

 [1]: https://tools.ietf.org/html/rfc4880#page-34
 [2]: http://www.gnupg.org/
 [3]: https://superuser.com/questions/360507/are-gpg-and-ssh-keys-interchangable