A question about expires attribute of Order Resource

After I finalize a order by send request with csr content to /finalize API.

Then I can get this response:


{
'Content-Length': '459',
 'Strict-Transport-Security': 'max-age=604800', 
'Cache-Control': 'public, max-age=0, no-cache',
 'Server': 'nginx',
 'Connection': 'keep-alive', 
'Link': '<https://acme-staging-v02.api.letsencrypt.org/directory>;rel="index"', 
'Location': 'https://acme-staging-v02.api.letsencrypt.org/acme/order/.../...', 
'Boulder-Requester': '17092284',
 'Date': 'Tue, 22 Dec 2020 03:52:47 GMT',
 'X-Frame-Options': 'DENY',
 'Content-Type': 'application/json', 
'Replay-Nonce': '0003NBeE3su_6fx2gelKMX6W6Wu7pLpevdEnd8OqWoYTII4'
}
{u'authorizations': [u'https://acme-staging-v02.api.letsencrypt.org/acme/authz-v3/....'],
 u'certificate': u'https://acme-staging-v02.api.letsencrypt.org/acme/cert/......',
 u'expires': u'2020-12-28T06:31:50Z',
 u'finalize': u'https://acme-staging-v02.api.letsencrypt.org/acme/finalize/...../....',
 u'identifiers': [{u'type': u'dns', u'value': .....'}],
 u'status': u'valid'}

PARAM: expires
is 2020-12-28T06:31:50Z .

I new this order at sometime of 2020-12-21.

Must I download the certificate before this time "2020-12-28T06:31:50Z "?

Once you successfully get a certificate generated, I'm not sure how long the certificate download link is valid. You can always download the certificate (and the intermediate certificate) anytime you want from https://crt.sh.

Ok, I should download the certificate as soon as possible.

Certificate download links are guaranteed to be valid for the entire lifetime of the certificate, which is significantly longer (90 days) than the lifetime of the order object (one week).

Just to be clear, that's a Boulder (as currently implemented) guarantee rather than an RFC 8555 protocol level guarantee, right? Like, that may not be the case with other ACME CAs?

Correct, nothing in RFC8555 or other regulations mandates a length of time for those URLs to work.