Is it possible to add other fields to user certificate?

Signature format:
```python
"python zeronet.py --debug cryptSign %s#bitmsg/%s %s 2>&1" % (auth_address, user_name, config.site_privatekey)
```
The first `%s` is obviously the user's public key. After that it is the portal type. The second `%s` is the user name.

Certificate format:
```python
data["users"][user_name] = "bitmsg,%s,%s" % (auth_address, sign)
```
The first item is certainly the portal type. The second item is the user's public key. The third item is the signature. The signature seems to be a signed message digest, so the whole message must be reconstructed in order to verify a signature (Is it [Schnorr-SHA256](https://github.com/sipa/secp256k1/blob/968e2f415a5e764d159ee03e95815ea11460854e/src/modules/schnorr/schnorr.md)?)

One possible way of adding additional fields to the certificate (i.e. registration time) is to append these information to the portal type or the user name, but I don't know how ZeroNet interprets the certificate.