ya, as i was laying in bed thinking about this (of course), I thought that it'd be more powerful to create an Certifier instance, that has some initial setup properties, like hostname, the private key, clock skew, etc.

```js
var certifier = new Certifier({
  hostname: 'foobar.com',
  privkey: PRIV_KEY,
  skew: 10 * 1000
});

//later...
certifier.certify({ pubkey: pubkey, principal: principal }, cb);
```