Get a part of the DN of the subject of this certificate.
Examples of a part might be the 'OU' (organizational unit) or the 'CN' (common name). Only the value of that part of the DN
is returned.
The string returned should be freed by the caller when no longer required.
| this | |
| part |
a DN type string or OID. |
|
the allocated part of the subject DN, or null if no such part is present. |