WIP: Libcurl backend

[goetzk]

Hi,
I'm after feedback on this change. Its only required in cases where the OS doesn't support SNI - in my case RHEL6 but I expect a similarly aged Debian/Ubuntu would see the same problem.

The main thing I want to know is if I should try and if/else it out so (for example) if WWW::Curl is available that is used instead of HTTP::Headers and SSLeay.

Do you need this change? If you see this, you need the changes:

bash-4.1$ lwp-request -U -S -e -d  https://test.datacite.org:443
GET https://test.datacite.org:443
User-Agent: lwp-request/5.827 libwww-perl/5.833

GET https://test.datacite.org:443 --> 500 Can't connect to test.datacite.org:443 (SSL connect attempt failed with unknown errorerror:14077410:SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure)
Content-Type: text/plain
Client-Date: Wed, 12 Sep 2018 22:54:39 GMT
Client-Warning: Internal response

If you see something like this, you should be fine unmodified:

bash-4.1$ lwp-request -U -S -e -d  https://researchdata.ands.org.au/api/doi/datacite
Enter username for ands at researchdata.ands.org.au:443: [username]
Password: 
GET https://researchdata.ands.org.au/api/doi/datacite
Authorization: Basic [big long string]
User-Agent: lwp-request/5.827 libwww-perl/5.833

GET https://researchdata.ands.org.au/api/doi/datacite --> 401 Unauthorized
GET https://researchdata.ands.org.au/api/doi/datacite --> 200 OK

We have used this code to mint several DOIs so the basic functionality is working.

[goetzk]

Looking at https://access.redhat.com/support/policy/updates/errata RHEL6 has 2 years of bug fix support left, so this code is unlikely to be used after that time.

From the Ubuntu side, only 14.04 is still supported but only for another ~7 months.
https://www.ubuntu.com/about/release-cycle

SNI fixes arrived in 6.0.7
https://metacpan.org/release/LWP-Protocol-https

I'm sure some other long term systems from different vendors are still out there, how many are running EPrints is another matter.