Add Load-balancing cookie support

[AnupamaSarjoshi]

Hi Richard,

As discussed in the forum https://coderunner.org.nz/mod/forum/discuss.php?d=667#p2726, we have implemented the fix
to support the Jobe back-ends that use cookies for sticky load-balancing, by creating a single curl object with support for cookies, and using it for all requests.

Could you please review? Have tested this by running the Jobe server on our AWS test environment, with load balancer generated cookies.

Thanks,
Anupama

[trampgeek]

Thanks Anupama. Another nice contribution.

[trampgeek]

Hi Anupama. We're getting log messages on the unlink($cookiefile) line saying the file doesn't exist. So presumably the fix is to prefix the unlink with '@'?

[timhunt]

In my bitter experience, any time you hide an error with @, you later regret it when you have a bug which is really hard to debug.

However, unlink is one of the safest times to do that, and it seems really common in other Moodle code, so I agree with your suggestion @trampgeek.

(A few places in Moodle do if (file_exists(...)) { unlink(...); } intead, but they are the exception.)

[AnupamaSarjoshi]

Thanks Richard and Tim for the fix. Sounds good :)
But the strange thing is we didn't get those messages in our logs - checked on both my local and our test environment.