va: Match CAA parameter tags case insensitively

[hablutzel1]

This makes the accounturi and validationmethods CAA parameter tags match case insensitively, so a differently cased tag such as AccountURI or ValidationMethods still restricts issuance instead of being treated as an unrecognized parameter.

From https://www.rfc-editor.org/rfc/rfc8659#section-4.1, stated for Property Tags:

Matching of tags is case insensitive.

That rule covers Property Tags (issue, issuewild, and so on). For the parameter tags carried inside an issue value, neither RFC 8659 nor RFC 8657 defines a comparison rule.

caaAccountURIMatches and caaValidationMethodMatches currently compare the parameter tag with == against the lowercase literals "accounturi" and "validationmethods". A differently cased tag does not match, so it is treated as an unrecognized parameter and the restriction is dropped. For accounturi the Property then matches any account, and for validationmethods any validation method is accepted, so in both cases a domain that intended to restrict issuance gets a false positive validation.

For reference, the same case being discussed in the PR for RFC 8657 support in the Open MPIC project, open-mpic/open-mpic-core-python#71 (comment)

[aarongable]

We have discussed this in the past, and would prefer not to merge this change.

Yes, there is some value in the "be strict in what you produce, and liberal in what you accept" philosophy. This PR would align with being liberal in what we accept.

However, we have seen no evidence that such mis-cased labels exist in the wild. As such, we are in a position to keep it that way. Becoming more liberal in what we accept will only allow the set of all CAA records to become messier. There's no reason to allow that when the current status quo is that CAA records have the correct capitalization.

If we're going to do anything differently, we would prefer to loudly fail on CAA records containing incorrectly capitalized parameter tags.

[hablutzel1]

If we're going to do anything differently, we would prefer to loudly fail on CAA records containing incorrectly capitalized parameter tags.

I agree with this approach as well.

Would you accept such a change? I can re-purpose the current PR.