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SSL, HTTPS, and HSTS

It's highly recommended to enable SSL/TLS on your server, both for the web app and email server.

Using Certbot to get a certificate

This doc will use https://letsencrypt.org to get a free SSL certificate for app.mydomain.com that's used by both Postfix and Nginx. Let's Encrypt provides Certbot, a tool to obtain and renew SSL certificates.

To install Certbot, please follow instructions on https://certbot.eff.org

Then obtain a certificate for Nginx, use the following command. You'd need to provide an email so Let's Encrypt can send you notifications when your domain is about to expire.

sudo certbot --nginx

After this step, you should see some "managed by Certbot" lines in /etc/nginx/sites-enabled/simplelogin

Securing Postfix

Now let's use the new certificate for our Postfix.

Replace these lines in /etc/postfix/main.cf

smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key

with

smtpd_tls_cert_file = /etc/letsencrypt/live/app.mydomain.com/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/app.mydomain.com/privkey.pem

Make sure to replace app.mydomain.com with your own domain.

Updating simplelogin.env

Make sure to change the URL in simplelogin.env to https://app.mydomain.com, otherwise not all page assets will load securely, and some functionality (e.g. Webauthn) will break. You will need to reload the docker containers for this to take effect.

HTTP Strict Transport Security (HSTS)

HSTS is an extra step you can take to protect your web app from certain man-in-the-middle attacks. It does this by specifying an amount of time (usually a really long one) for which you should only accept HTTPS connections, not HTTP ones. Because of this you should only enable HSTS once you know HTTPS is working correctly, as otherwise you may find your browser blocking you from accessing your own web app.

To enable HSTS, add the following line to the server block of the Nginx configuration file:

add_header Strict-Transport-Security "max-age: 31536000; includeSubDomains" always;

(The max-age is the time in seconds to not permit a HTTP connection, in this case it's one year.)

Now, reload Nginx:

sudo systemctl reload nginx