[det]load_private_key(+Stream,
+Password, -PrivateKey)Load a private key PrivateKey from the given stream Stream,
using Password to decrypt the key if it is encrypted. Note
that the password is currently only supported for PEM files. DER-encoded
keys which are password protected will not load. The key must be an RSA
or EC key. DH and DSA keys are not supported, and PrivateKey
will be bound to an atom (dh_key or dsa_key) if you try and load such a
key. Otherwise PrivateKey will be unified with private_key(KeyTerm)
where KeyTerm is an rsa/8 term
representing an RSA key, or ec/3 for EC
keys.