For TLS-based EAP types, such as TLS, TTLS, and PEAP, this
optional parameter specifies the name of the file containing the server's
private key.
The private key file must be in PEM or ASN1 format,
depending on the setting of the
EAPTLS_CertificateType
parameter.
It can be
located in the same file as the server certificate
(EAPTLS_CertificateFile
). If the private key is
encrypted, which is usually the case,
EAPTLS_PrivateKeyPassword
is the key to decrypt
it.
Special characters are supported.