The filename indicates the file that contains the client's identity. An identity consists of the client certificate, the corresponding
private key, and, optionally, the certificates of the intermediary certificate authorities.
If the private key is encrypted, use the identity_password option to specify a password. See identity_password.
MobiLink clients cannot authenticate directly to MobiLink using client-side certificates. They can only be used to authenticate
to third-party servers and proxies that have been configured to accept client-side certificate authentication, and are sitting
between the client and MobiLink server.