I have been looking at the steps required to migrate the WildFly Elytron integration to Undertow 3 from Undertow 2.
Overall it seems minimal changes are required but I was thinking if there could be an opportunity to evolve the API within Undertow 2 making migration to 3 easier in the future.
One example being on SSSessionInfo we make use of the following method: -
void renegotiate(HttpServerExchange exchange, SslClientAuthMode sslClientAuthMode) throws IOException;
which has now been changed to: -
void renegotiate(HttpServerExchange exchange, ClientAuth sslClientAuthMode) throws IOException;
The first form is making use of Xnio API and the second is using Netty API.
If this was deprecated in Undertow 2 and a pure Undertow variant added it could be usable both in 2 and 3.