Add property to enable SPDY or HTTP2 in Undertow

[eddumelendez]

See gh-3350

[philwebb]

See #3350

[wilkinsona]

I don't like the server.undertow.option property that was proposed in #3350 and implemented here for a couple of reasons:

1. There are a lot of options that could be set, so only supporting SPDY or HTTP2 feels rather strange. Also, some options have configurable values that couldn't be set using this approach.
2. HTTP2 (and SPDY) isn't something that's Undertow-specific. Jetty 9.3 (9.2 is the default at the moment but we do support 9.3 and have a sample for it) also supports HTTP2 and Tomcat will in 9.0.

I think it's worth taking a step back and considering the broader picture for HTTP2 rather than focussing specifically on Undertow and the details of how it's enabled when using Undertow.

[cbelleza]

Nowadays SPDY/HTTP2 is a mandatory resource to get applications safer and faster, having an option by properties is much easier than having a custom EmbeddedFactory to enable it.

For a long while I have been missing this option in Spring Boot and I agree with @wilkinsona this should not only be able for Undertow as another web servers.

Opening a property to set any value to web server I agree is dangerous, but an enum to manage SPDY or HTTP2 is a good option.

What I meant here is that Spring Boot should go further that only allowing to code it.

[wilkinsona]

I'm going to close this one is the approach that's been implemented isn't the one that we want to take for enabling HTTP2.

[herau]

@wilkinsona any news about this topic ? Did you have a common way to enable HTTP2 ?

[wilkinsona]

No news at the moment. #3350 is still open.