Updated 21.07.2016 reflecting changes since Charles 3.10
For enabling plain text communication on SSL connections Charles act as a Man in the Middle. After you have managed your device to communicate via Charles http proxy, you need to download and install certificate from your running instance of Charles, its generated and signed by a Charles Root Certificate.
Basically there are two ways possible (I prefer the first one):
Download and install directly on device
Device has to be configured to communicate via Charles!
- start browser
- open http://charlesproxy.com/getssl
- certificate download will be started
- confirm insertion dialog
Save the certificate from Charles UI
- save the certificate via "Help -> SSL Proxying -> Save Charles Root Certificate.."
- put it on a device (via adb push, email ....) and click on the file in order to install it.
Note 1: After install the certificate you will be forced to create a security Pin/Pattern/Password for the device.
Note 2: Since Charles v3.10 single SSL Root Certificates aren't supported anymore.