add arg --outfile

[btwe]

I have acme-tiny integrated as a systemd service + a timer. I find it handy to also specify an outfile, where the signed certificate + chain should be written to.

Of course, the default behaviour remains, which prints the signed cert to STDOUT.

Output with --outfile /etc/pki/acme/domainA.cert:

acme_tiny.py[55382]: Certificate signed!
acme_tiny.py[55382]: Writing signed certificate to /etc/pki/acme/domainA.cert
systemd[1]: acme.service: Succeeded.

Output without --outfile:

acme_tiny.py[55468]: Signing certificate...
acme_tiny.py[55468]: Certificate signed!
acme_tiny.py[55468]: Writing signed certificate to STDOUT
acme_tiny.py[55468]: -----BEGIN CERTIFICATE-----
acme_tiny.py[55468]: MIIHPTCCBiWgAwIBAgITAPpExoEu268QebqRtct2tMvL2jANBgkqhkiG9w0BAQsF
...
acme_tiny.py[55468]: oZ2lS38fL18Aon458fbc0BPHtenfhKj5
acme_tiny.py[55468]: -----END CERTIFICATE-----
systemd[1]: acme.service: Succeeded.

[diafygi]

@btwe It looks like this pull request puts acme-tiny over the 200 line limit, so I'm not going to merge it for now. However, I'll keep this pull request open if I decide to increase the line limit, I can merge this.

[btwe]

I understand, this would change the selling point. But let me try to show another aspect: The line count limit itself does not increase readability. I think you could somehow squeeze the output conditional into a single line. But readability of the source is also a selling point for acme-tiny. My little experience is that trying to stick to pep8 might also increase readability with the human eye, but of course this would blow the 200 lines by a lot (~70)

Don't get me wrong, I do not intend to convince you of changing anything. I know how to patch this PR in on my side; also thanks to the small code base, it is very easy to do this.

So, thanks a lot for your work on acme-tiny and publishing it. I have this PR on watch so I'll get updated 👍