Fix wildcard match to ACME domains in cluster mode

[oldmantaiter]

What does this PR do?

• Allows matching of hosts like x.traefik.wtf to ACME wildcard
  certs *.traefik.wtf

Motivation

• Tested wildcard acme v2 and noticed that it was not properly selecting my wildcard domains

More

• Added/updated tests
• Added/updated documentation

Additional Notes

[emilevauge]

@oldmantaiter could you explain more in details why you added those lines in getCertificateForDomain() ?

if strings.HasPrefix(domain, "*.") {
	selector := "^" + strings.Replace(domain, "*.", "[^\\.]*\\.", -1) + "$"
	if domainCheck, _ := regexp.MatchString(selector, domainToFind); domainCheck {
		return domainsCertificate, true
	}
}

[oldmantaiter]

@emilevauge for sure.

I was testing the new ACMEv2 merge and created a certificate for (as an example) *.foo.bar and have backends that route based on Host:x.foo.bar or Host:y.foo.bar. These were not properly getting the stored ACME wildcard cert because this function only looked for an exact string match

[dtomcej]

@emilevauge This code snippet has been repeated in the acme package 3x already, and in server.go, do you think that we should refactor this to be a more unified function, to check for matches better? rather than re-duplicating code?

[oldmantaiter]

@dtomcej I noticed the same, I can combine if that is easier

[nmengin]

I am agree with @dtomcej .

I guess we can transform the list of DomainCertificate into a map[string]*tls.Certificate instead of a []string in the loop instruction (by using the metod Domain.ToStrArray as keys and the DomainCertificate.Certificate as values).

Then, we can use acme.searchProvidedCertificateForDomains method instead of copy/paste the regexp matching.

@oldmantaiter Do you think you can do it? Or do you need some help?

[nmengin]

@oldmantaiter

Many thanks for your PR.
Because this fix is very important, I did the pattern matching refacto in the way to generate quickly a new Release Candidate.

[oldmantaiter]

@nmengin Thanks. There is one more place I saw this pattern matching code (provider/acme/provider.go) so I was going to put the function inside provider/acme and reference it from the acme package.

[nmengin]

@oldmantaiter I saw it too and I am currently analyzing a solution to integrate all of them.

I think it will be in an other PR.

Many thanks for your feedback 👍

[mmatur]

LGTM 👏

[nmengin]

LGTM

[juliens]

LGTM