The PrivateKey property specifies the path to the private
key file used to authenticate the user. The private key is used in
combination with the value of the UserName property to provide
credentials to an SSH server. If public/private key authentication is
not required by the server, this property is should be set to an empty
string.
The PrivateKey property value can use environment variables
enclosed in percent symbols, and the path to the private key file will
be normalized. It is recommended you always use an absolute path to
the private key file. If you do not include a path, it will use the
current working directory for the process. This can produce
inconsistent results because the current working directory for a
process is a global value and it can be changed at any time.
The private key file name must resolve to a text file which
can be read by the current process. If the file does not exist, or it
does not specify a PEM formatted file which contains an RSA or OpenSSH
private key, the connection will fail and the last error code will be
set to stErrorInvalidPrivateKey.