crypto/tls: missing some cipher suite constants

[rutledgechinfeman]

This file has a list of constants for TLS cipher suites:

https://golang.org/src/crypto/tls/cipher_suites.go

The list is incomplete, for example the ChaCha20-Poly1305 ciphers are missing. It would be useful to either (a) complete the list of ciphers and, or (b) document how the list of ciphers is curated.

If (a), there should also be some mechanism to keep the list up-to-date over time.

[minux]

I think the criteria is simply it includes what the package supports.

[bradfitz]

@agl, do you want [somebody else] to document that this is only those supported by the crypto/tls package, or do you want [somebody else] to auto-generate those constants, perhaps with go generate from https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4 ?

[agl]

I don't think that we should try to include every constant in that package because of the large number of them. I'll send out a change to document this in a sec.

[gopherbot]

CL https://golang.org/cl/20551 mentions this issue.