Verify we’re running the latest version of Debian

lsb_release -a
No LSB modules are available.
Distributor ID:	Debian
Description:	Debian GNU/Linux 11 (bullseye)
Release:	11
Codename:	bullseye

Become root

sudo su

Update packages

apt update && apt upgrade -y

Install the Squid package that has openssl configured and enabled

apt install squid-openssl

Create a local CA, using a 4096-bit key and SHA-2 hashing. This one is good for the next 10 years

openssl req -new -newkey rsa:4096 -sha256 -days 3653 -nodes -x509 -keyout /etc/squid/CA.key -out /etc/squid/CA.crt

Combine the key and cert in to a single file for convenience

cat CA.key CA.crt > CA.pem

Initialize the directory used for minted certs and set permissions so squid owns it

/usr/lib/squid/security_file_certgen -c -s /var/spool/squid/ssl_db -M 4MB
chown -R proxy:proxy /var/spool/squid

Finally, configure Squid to use HTTPS

http_port 3128 ssl-bump cert=/etc/squid/CA.pem generate-host-certificates=on options=NO_SSLv3
ssl_bump bump all

Restart Squid

service squid restart

Test connections by configuring 3128. Note the certificate from the CA, good for 10 years:

export https_proxy=http://localhost:3128

curl -v --cacert CA.crt  https://teapotme.com 

* Uses proxy env variable https_proxy == 'http://localhost:3128'
*   Trying ::1:3128...
* Connected to localhost (::1) port 3128 (#0)
* allocate connect buffer!
* Establish HTTP proxy tunnel to teapotme.com:443
> CONNECT teapotme.com:443 HTTP/1.1
> Host: teapotme.com:443
> User-Agent: curl/7.74.0
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 200 Connection established
< 
* Proxy replied 200 to CONNECT request
* CONNECT phase completed!
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*  CAfile: CA.crt
*  CApath: /etc/ssl/certs
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* CONNECT phase completed!
* CONNECT phase completed!
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
* TLSv1.3 (IN), TLS handshake, Certificate (11):
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
* TLSv1.3 (IN), TLS handshake, Finished (20):
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.3 (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* ALPN, server did not agree to a protocol
* Server certificate:
*  subject: CN=teapotme.com
*  start date: Nov  6 04:03:48 2022 GMT
*  expire date: Nov  6 04:03:48 2032 GMT
*  subjectAltName: host "teapotme.com" matched cert's "teapotme.com"
*  issuer: C=AU; ST=Some-State; O=Internet Widgits Pty Ltd; CN=localhost
*  SSL certificate verify ok.
> GET / HTTP/1.1
> Host: teapotme.com
> User-Agent: curl/7.74.0
> Accept: */*
> 
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* old SSL session ID is stale, removing
* Mark bundle as not supporting multiuse
< HTTP/1.1 418 I'm a teapot
< Server: nginx
< Date: Sun, 06 Nov 2022 04:08:13 GMT
< Content-Type: application/json
< Content-Length: 483
< X-Cache: MISS from test-1
< X-Cache-Lookup: MISS from test-1:3128
< Via: 1.1 test-1 (squid/4.13)
< Connection: keep-alive
< 
{
    "host": "teapotme.com",
    "user-agent": "curl/7.74.0",
    "x-forwarded-for": "::1, 35.233.234.155, 172.17.0.1",
    "x-forwarded-proto": "https",
}