Fix expired certificate errors on legacy Android versions

If you have an old Android device, you've probably come across expired certificate errors. These legacy Android versions no longer receive updates, and their certificates also not. However, you can update them manually.

The two main certificates you need are DigiCert Global Root G2 and ISRG Root X1. Download the .PEM files here and here, respectively. You'll need to scroll down and find the certificate with the exact same name I specified before. With these two files stored on the device, it's time to install them.

The installation process varies across devices. On Android 4.4, go to Settings, Security, Install from SD card (actually, you don't need to have a SD card). Select the files, one at time, and you're done.

Android may show warnings that the network may be being monitored, but don't worry, it's not. Ignore these warnings, since it's not possible to disable them.