JNI: wrap wolfSSL_set_tls13_secret_cb() in WolfSSLSession.setTls13SecretCb()

[cconlon]

This PR wraps the native wolfSSL API wolfSSL_set_tls13_secret_cb() inside the WolfSSLSession class. This allows JNI-level users to write and register a TLS 1.3 secret callback for use with Wireshark.

Native wolfSSL needs to be compiled with -DHAVE_SECRET_CALLBACK, ie:

cd wolfssl-X.X.X
./configure --enable-jni CFLAGS="-DHAVE_SECRET_CALLBACK"
make
sudo make install

Java applications need to implement the com.wolfssl.WolfSSLTls13SecretCallback interface, for example:

class MyTls13SecretCb implements WolfSSLTls13SecretCallback
{
    public int tls13SecretCallback(WolfSSLSession ssl, int id,
        byte[] secret, Object ctx)
    {
        /* Implement callback logic, see examples/MyTls13ClientCallback.java for example */
    }
}

Then provide an instance of that to WolfSSLSession.setTls13SecretCb(). For example:

WolfSSLSession ssl = ...
MyTls13SecretCb cb = new MyTls13SecretCb();

ssl.keepArrays();
ssl.setTls13SecretCb(cb, null);

For an example of using the TLS 1.3 secret callback, see the example JNI client (examples/Client.java, examples/MyTls13SecretCallback.java).

The example JNI client and server can be connected against each other with the client using the example TLS 1.3 secret callback using the following. Note that like mentioned above, native wolfSSL must be compiled with -DHAVE_SECRET_CALLBACK.

./examples/server.sh -v 4
./examples/client.sh -tls13secretcb sslkeylog.log -v 4
...
(sslkeylog.log should be available under examples/build/sslkeylog.log)