crypto/tls: don't require Config to set MinVersion = TLS13 when using QUIC

[marten-seemann]

What version of Go are you using (go version)?

$ go version
go version go1.21.0 darwin/arm64

Does this issue reproduce with the latest release?

Yes

What did you do?

Using QUIC currently requires passing in a tls.Config that defines TLS 1.3 as its minimum TLS version. This makes it difficult to run a TLS/TCP and QUIC service using the same tls.Config, since the TLS/TCP service potentially doesn't want to limit the available TLS versions to TLS 1.3.

The workaround applied by quic-go at the moment is cloning the config and setting TLS 1.3, but this has various downsides, as described by @dneil in #63691.

What did you expect to see?

crypto/tls knows when a Config is used for QUIC. Instead of requiring MinVersion to be set explicitly, it should treat any config as if this field was set to TLS 1.3.

[gopherbot]

Change https://go.dev/cl/537575 mentions this issue: crypto/tls: don't require Config.Minversion to be set when using QUIC

[neild]

This seems reasonable to me. There isn't any benefit I can see to forcing the user to set MinVersion, and implicitly upping it it to 1.3 for QUIC connections lets the same Config be reused for QUIC and non-QUIC cases.