Document and throw an error to help people with CURLOPT_SSL_VERIFYPEER issues

[akaSyntaax]

Issue Summary

If I try to send an email trough the sendgrid-php api I only get a timeout after a while, the email doesn't get send. There are no errors thrown. This issue happened after an update from version 3.9.0 to 3.9.1.

Steps to Reproduce

1. Try to send a simple email (from the sendgrid-php repository for example)

Technical details:

• php-http-client Version: 3.9.1 (commit 56d046a)
• PHP Version: 7.1.15-1

[thinkingserious]

Hello @akaSyntaax,

I believe the issue is probably due to this: https://github.com/sendgrid/php-http-client/blob/master/lib/Client.php#L189

If you set that value to false it will work, but that would be insecure, per this issue: #81. The better fix would be to update your *.pem path, like so: https://stackoverflow.com/questions/18971983/curl-requires-curlopt-ssl-verifypeer-false

With Best Regards,

Elmer

[thinkingserious]

That said, we need to update the SDK to throw an error that specifically states the peer is not verified.

[akaSyntaax]

Hello @thinkingserious,

I updated my *.pem path as you said and this resolved my issue.
Thank you very much!

Kind regards,
Hendrik Lübke (akaSyntaax)

[thinkingserious]

Thanks for the follow up @akaSyntaax.

I'm re-opening so we can properly document this and create a helpful error message.

[colinodell]

I have introduced three possible PRs to address this:

Two PRs to alert the user to an issue:

• feat: Throw an InvalidRequest whenever a curl request fails #103 will throw an exception which can be caught and handled accordingly
• Trigger an E_USER_ERROR whenever a curl request fails (#90) #104 will trigger an E_USER_ERROR

One PR (#105) to help users whose PHP instance is having trouble locating the CA bundle.