Added docs on how to configure the reverse proxy for a subfolder & Documented the usage of X-Forwared-Prefix

[jbtronics]

If you want to put a symfony application behind a reverse proxy which is configured the application in a subfolder, then this is supported by setting the non-standard X-Forwarded-Prefix HTTP header. This was already added in Symfony 5.2. However, this is nowhere documented and no good solution on how to achieve this goal is found on the internet. This commit adds documentation on how to use this header.

This should apply to all Symfony versions (at least from 5.4 upwards)

[javiereguiluz]

Let me ask for a quick review to @dbu because I know that David has battled with many proxies, so maybe he can share some insights here. Thanks!

[dbu]

seems good to me. i never needed to use this functionality myself, but it makes sense.

i think the documentation section could be a bit more concrete to avoid confusion

[dbu]

if i understand correctly, this is about the proxy routing to symfony for /subpath, but symfony itself running on /? in a way this is the only thing that makes sense for this documentation, nonetheless i would make that more explicit. you could start with the example and explicitly explain that the symfony application runs at /, and give the example of what absolute paths/urls should be.

[javiereguiluz]

@jbtronics if possible, please add a phrase or two as a short introduction to the exact problem that this solves, as asked by David. Thanks!

[jbtronics]

I added an example. I hope the explaination is now a bit more clear and explict. @dbu

[dbu]

looks correct and understandable now 👍

[jbtronics]

@javiereguiluz I've rewrote the first sentences. I hope its more clear now.

[javiereguiluz]

Jan, this is finally merged! Thanks a lot for contributing this to the docs. It's an uncommon feature ... but folks using this will definitely appreciate your explanation. Thanks also to David for the review!