[redprince]

> Instead, trying to access a blocked website gets me a wrong/unsafe certificate warning followed by a Fortinet/Fortiguard blockpage when I click continue.

This is likely the Fortigate SSL/TLS deep inspection (<https://docs.fortinet.com/document/fortigate/7.6.0/best-prac...>). In short: The Fortigate conducts an organizationally sanctioned MITM attack on your web browsing. You would not get any warning if the public key of the certification authority on the Fortigate had been installed on your client. In corporate Windows environments this is usually done via group policies.

Some websites may appear not to be subjected to deep inspection if those websites were exempt from SSL/TLS deep inspection. They'd be using SNI or the CN / SAN contents of the certificate presented by the website to make a policy decision against an allow or deny list of sites.

Another possible scenario would be that you have the MITM CA installed but the block page your browser gets redirected to by the Fortigate was signed by another CA / self signed. But that would certainly be a misconfiguration on the Fortigate.

Anyway. Your web browser allows you to inspect the certificate and more crucially the certificate chain used to verify the validity of a certificate. Look at the root certificate when you suspect a connection to be inspected. If the name of the root CA isn't already giving it away, you should be able to verify that it is a benign public CA by googling for it.

Given the rest of your experience, I'm guessing the IT staff wants to increase control over what applications and sites can be used over the school network. It is rather easy to detect and block DoH and other possible filter evasions when you can decrypt all communication.

> Also I find it disconcerting that my school blocks hrw.org (i. e. human rights watch) which I believe sends a wrong message.

You can check how a site is categorized by the Fortigate here: https://www.fortiguard.com/webfilter

Currently https://www.hrw.org/ is categorized as "Advocacy Organizations" in the group "Adult / Mature Content". I'm going to guess the whole "Adult / Mature Content" group has been blocked and you found a striking example of over blocking.

Now... what can you do about it? The easiest and least troublesome solution would be to just ignore the nosy IT infrastructure and use the school computers and their network just for the work assigned to you. I'm guessing you have unfiltered access to the Internet off campus anyway. Or you could tether you device to your mobile phone and bypass all filtering that way.

Subverting the school's attempts to limit your access is certainly a possibility given sufficient tenacity to learn and a certain kind of creativity with a tendency to cause mischief. But I'll leave it to you to figure out the details. When your actions get you into trouble: You have asked for it. Act accordingly.