Reads a passphrase using readpassphrase(3), returning it as a String.
Internally uses a buffer of PASSWORD_LEN bytes, allowing for passwords
up to PASSWORD_LEN - 1 characters (including the null terminator.)
Reads a passphrase using readpassphrase(3) into the passed buffer.
Returns a String consisting of the same memory from the buffer. If
the zeroize feature is enabled (which it is by default), memory is
cleared on errors.