Add a modifier for changing HTTP headers

[ameshkov]

Consider adding a modifier that allows modifying HTTP headers. This could be pretty much the same as $replace, but for HTTP headers.

There are several applications for such a header:

1. Emulating a cookie (can help with cookie notices). On the other hand, there's already a scriptlet for that.
2. Change user agent in some requests.
3. Change referrer.
4. Set own policies, etc.

You can do A LOT with this so it must be a trusted-level modifier.

We need to see how many upvotes this feature request gets.

Discussion: https://github.com/AdguardTeam/AdguardForWindows/issues/1720

[AdamWr]

It would be nice to have such feature. Maybe it's not ad related but some websites (for example this one - https://github.com/AdguardTeam/AdguardFilters/issues/162841) displays a different content basing on some headers (it seems that in this case they check accept-language header if it starts with pl, and if not, other content is displayed) to see full content, it's necessary to change browser language or use extension to modify it.

[ameshkov]

Good example, but we'll need a couple more to justify this. Please provide more examples so that we could figure out how to implement this.

[AdamWr]

Another case is Twitch and ads which are currently not blocked in Brave browser. It looks like that if we could change request header sec-ch-ua (for gql.twitch.tv/gql request) to something like (it's from Chrome):

"Not;A=Brand";v="99", "Google Chrome";v="139","Chromium";v="139"

(in Brave it's "Not)A;Brand";v="8", "Chromium";v="138", "Brave";v="138") then ads would be blocked. Removing this header causes that ads are not blocked also in other browsers, so it's not a solution in this case.

Related issue - https://github.com/AdguardTeam/AdGuardExtra/issues/599#issuecomment-3009710977

In general, it would be nice to have similar options like in Requestly extension - https://chromewebstore.google.com/detail/requestly-supercharge-you/mdnleldcmiljblolnjhpnblkcekpdkpa where is possible to override request and response headers.

So we could use something like (commas probably should be escaped, like in other modifiers):

||gql.twitch.tv/gql$setheader=request:sec-ch-ua:"Not;A=Brand";v="99", "Google Chrome";v="139", "Chromium";v="139",app=brave.exe

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Also an option to just replace some value would be nice, for example:

||gql.twitch.tv/gql$replaceheader=request:sec-ch-ua:/Brave/Google Chrome/