I am developing an HTTPS client on the ST8082TR chip. I experienced problems when connecting to Apache HTTPS servers since version 2.4.10-10+deb8u8 or 2.2.22-13+deb7u8.
The reason is that since this update, the Apache module reqtimeout is enabled by default. The Open AT Application does not have sufficient time to connect before apache respond with 408 code: timeout.
To bypass this, the server has to be configured with a greater timeout. In /etc/apache2/mods-available/reqtimeout.conf, line 19, replace
I hope that can spare you some debugging time.
Have a nice day !