#35 - update cert.pem
I submitted the same thing upstream: https://github.com/AuthorizeNet/sdk-php/pull/466, but as I noted in the related issue there, I don't understand how you're supposed to test it ahead of time since it sounds like both sandbox and prod are switching the same time. I checked and the sandbox still seems to have the Entrust cert (see below). But I can see that the new cert.pem has both the old and new certs.
> openssl s_client -connect apitest.authorize.net:443 -showcerts
CONNECTED(000001BC)
depth=2 C = US, O = "Entrust, Inc.", OU = See www.entrust.net/legal-terms, OU = "(c) 2009 Entrust, Inc. - for authorized use only", CN = Entrust Root Certification Authority - G2
verify return:1
depth=1 C = US, O = "Entrust, Inc.", OU = See www.entrust.net/legal-terms, OU = "(c) 2012 Entrust, Inc. - for authorized use only", CN = Entrust Certification Authority - L1K
verify return:1
depth=0 C = US, ST = California, L = Foster City, O = Authorize.Net, CN = *.authorize.net
verify return:1