From Pi My Life Up:
This Raspberry Pi SSL certificate project will walk you through the steps to installing and setting up the Let’s Encrypt Certbot client on the Pi. This Certbot client allows the user to grab a SSL certificate from Let’s Encrypt by either utilizing your own web server or by running its own temporary server.
Let’s Encrypt is the best way to easily obtain a secure and certified SSL certificate for your Raspberry Pi completely free. Before you get started with setting up SSL on your Raspberry Pi, make sure that you have a domain name already set up and pointed at your IP address as an IP Address cannot have a certified SSL Certificate.
If you are using Cloudflare as your DNS provider, then make sure you have it set to bypass Cloudflare as it hides your IP address meaning the Let’s Encrypt tool will fail to verify your Raspberry Pi’s IP address and generate it a SSL certificate.
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