private key not available for client_cert_cb

[George <whippet0@xxxxxxxxx>]

    Hi,
    
       I'm new to OpenSSL and am trying to set up mutual authentication
    in a client. The client is setup with OpenSSL 1.0.2u. and the
    client's certificate + private key is stored on a Smart Card.  When
    the client receives a certificate request from the server during the
    mutual authentication handshake, the OpenSSL client_cert_cb
    callback function is automatically invoked. The problem is that client_cert_cb
    requires a private key. Unfortunately, it is not possible to get a
    private key from a Smart Card. Is there a way to send a certificate
    to the server without needing the private key?
    
    I'm setting up the callback function with:
     
    void
      SSL_CTX_set_client_cert_cb(SSL_CTX *ctx, int (*client_cert_cb)(SSL
      *ssl, X509 **x509, EVP_PKEY **pkey));
    
    
    Here is a sample of what my code looks like when I set this up:
    
    SSL_CTX_set_client_cert_cb(context,
      openSSLClientAuthenticationCallBack);
      
      int openSSLClientAuthenticationCallBack(SSL *ssl, X509
      **x509, EVP_PKEY **pkey)
      {
      . . .
      }
    
    
    I can access the Smart Card using the PKCS#11 interface and I'm able
    to get the certificate and sign it, etc. However, I cannot get the
    actual private key from the Smart Card.
    
    Does anyone know how I can get around this problem?
    
    
    Thanks,
    George