Should provide API to support export of testing status

From the original Debian bug:

On Thu, 05 Sep 2019 11:16:39 +0200 Ansgar Burchardt <email address hidden> wrote:
> Package: dkimpy-milter
> Version: 1.0.1-1
> Severity: wishlist
> Tags: upstream
>
> Hi,
>
> a recent mail to -devel@ resulted in the following header from dkimpy-milter:
>
> Authentication-Results: [...]; dkim=fail (Bad 1024 bit rsa-sha256 signature.) header.d=[...] header.a=rsa-sha256
>
> However the domain (or key) is in testing mode (t=y):
>
> +---
> | [...]._domainkey.[...] 1513 IN TXT "v=DKIM1; t=y; k=rsa; p=[...]"
> +---[ $ dig TXT a._domainkey.[...] ]
>
> It would be nice if dkimpy-milter would report when a domain is
> testing DKIM.

I checked and the python3-dkim doesn't provide an API to support this request. In theory I could retrieve the key record in the milter and check, but that seems like a poor way to go about it. I've cloned the bug to dkimpy.

Also, there's no programmatic way to report this in an A-R header. Currently it would have to be in a (comment) which isn't so great either.

For background, all through the period Yahoo! was supporting the predecessor DomainKeys protocol they always had t=y, which was ridiculous and people started ignoring the flag. In the decade I've been maintaining dkimpy this is the first time it's come up.

Still, it's a reasonable request and dkimpy should support the protocol as defined.

Scott K