[Netty 5] Early data for TLSv1.3

[normanmaurer]

TLSv1.3 supports the concept of early data. We should add support for it.

[rkapsi]

Is there anything special that needs to happen other than using Session Tickets (or IDs) in conjunction with TLS 1.3? I'm speaking in terms of server side, a client might require some extra work.

[rkapsi]

Adding link to this SSL_read_early_data for future reference.

[rkapsi]

@normanmaurer I'd like to take a stab at this.

[rkapsi]

To give a little update. The TCN side is pretty straight forward. BoringSSL uses a slightly different API than OpenSSL but I believe Boring's API can be "massaged" to emulate the OpenSSL API/behavior. I have that stuff compiling and hypothetically working.

Now, SSLEngine#wrap/unwrap is where the skeletons lie. I'm afraid none of the state and logic flow hold in the context of early data. It'll take a few 🍷 to untangle it.

[hyperxpro]

@rkapsi Any updates?

[hyperxpro]

Also, we need a way to notify SslHandler that TLS was established using the Early Data method. Because there are some weaknesses to this. Maybe something like SslHandler#isEarlyData would do the job.