View source for Postgres x509 tls certs

https://dba.stackexchange.com/questions/36416/what-is-the-best-way-to-store-x509-certificate-in-postgresql-database

```
CREATE OR REPLACE FUNCTION issuer(x509table) returns text 
LANGUAGE SQL IMMUTABLE AS $$
    select issuer_cn FROM extract_x509info($1.x509data);
$$;
```

This can then be found by
```
SELECT x.issuer FROM x509table x;  --works
```


Auth
- https://www.postgresql.org/docs/current/auth-cert.html