What exactly does the variable SERVER_PROTOCOL actually contain (Apache 2.4)?

Binarus asked:

I have a website served by Apache 2.4 which should serve all contents via HTTPS. I already have appropriate redirections in place which work correctly, but don’t catch any pathological case. I wanted to improve that situation, and, when doing my homework, came across the following example in this document:

    Redirect "/admin/" "https://www.example.com/admin/"

I slightly modified this to reflect my situation:

    Redirect "/" "https://www.example.com/"

Now, when trying to view any URL from my site, the browser goes into an infinite redirection loop.

I am suspecting that the example actually is wrong. SERVER_PROTOCOL does not seem to contain the value HTTPS under any circumstances. Instead, according to what I have read in other articles, it contains things like HTTP/1.1 (as the name would let expect).

So my question is: What exactly does SERVER_PROTOCOL contain under what circumstances / in what context? And what could be the reason that Apache’s official documentation website is the only one I have found during several hours of research that lists HTTPS as a possible value of SERVER_PROTOCOL?

My answer:

Congratulations, you found an error in the Apache documentation. Consider reporting it.

As for your immediate problem, you appear to be looking for REQUEST_SCHEME, which will contain

The scheme part of the request’s URI

for instance, http or https.

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