Cant get DNS over HTTPS to work, is this even possible?

[levelek1337]

tried like this

IRequestContext ctx = Cef.GetGlobalRequestContext();
if (ctx == null) return;

string error;

Log(ctx.SetPreference("dns_over_https.mode", "secure", out error), "dns_over_https_mode", error);
Log(ctx.SetPreference("dns_over_https.templates", "https://dns.adguard-dns.com/dns-query", out error), "dns_over_https_templates", error);

//

like this :

settings.CefCommandLineArgs.Add("use-dns-over-https", "1");
settings.CefCommandLineArgs.Add("dns-over-https-mode", "secure");
settings.CefCommandLineArgs.Add("dns-over-https-templates", "https://dns.adguard-dns.com/dns-query");

enable features : "DnsOverHttps"

and like this :

settings.CefCommandLineArgs.Add("force-fieldtrial-params", "DoHTrial.Group1:Fallback/true/Templates/https%3A%2F%2Fdns.adguard-dns.com%2Fdns-query");

enable features : "DnsOverHttps<DoHTrial"

[cookesan]

There is not a CefSharp-specific DNS-over-HTTPS API that I can see. CefSharp can do two relevant things here:

1. Pass command-line switches to CEF before Cef.Initialize().
2. Set request-context preferences, but only if CEF/Chromium exposes that preference as settable.

For the preference route, I would first check whether CEF says the preference is settable:

using (var ctx = Cef.GetGlobalRequestContext())
{
    var canSetMode = ctx.CanSetPreference("dns_over_https.mode");
    var canSetTemplates = ctx.CanSetPreference("dns_over_https.templates");

    string error;
    var modeSet = ctx.SetPreference("dns_over_https.mode", "secure", out error);
    // log canSetMode, modeSet, and error
}

The timing matters. CefSharp's own comments point to IBrowserProcessHandler.OnContextInitialized() as the first place you can access the global request context and set preferences. For a custom RequestContext, RequestContextHandler.OnRequestContextInitialized() is the right place because it runs before that context's first request. Calling this later can be too late for network-stack behavior, and preferences set via command line usually cannot be changed afterward.

For the command-line route, make sure the switches are added to CefSettings.CefCommandLineArgs before Cef.Initialize(). But I would treat those switches as CEF/Chromium-version dependent. The CefSharp example comments explicitly warn that Chromium switches may change between versions and are not all relevant to CefSharp/CEF.

So the practical answer is: CefSharp can pass the settings through, but if CanSetPreference is false or SetPreference returns an error for those dns_over_https.* names, then it is not a CefSharp syntax problem. It means the embedded CEF build is not exposing those knobs as mutable preferences in that context.

[levelek1337]

Thank you for the detailed response. My code is already correct based on what you said. I tested three CEF builds, and none of them allow you to set this as a preference, so for anyone reading this in the future, the answer is no it’s not possible unless someone will make some fork of CEF with it.

[amaitland]

As this isn't a CefSharp specific feature, the best place to ask is https://www.magpcss.org/ceforum/index.php

If you are new to the project please make sure to read the first few paragraphs of https://github.com/cefsharp/CefSharp/wiki/General-Usage