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Changing the User Agent string in UWP WebView

2018 Oct 23, 9:32

There's no perfect way to change the user agent string for the UWP WebView (x-ms-webview in HTML, Windows.UI.Xaml.Controls.WebView in XAML, and Windows.Web.UI.Interop.WebViewControl in Win32) but there are two imperfect methods folks end up using.

The first is to call UrlMkSetSessionOption. This is an old public API that allows you to configure various arcane options including one that is the default user agent string for requests running through urlmon. This API is allowed by the Microsoft Store for UWP apps. The change it applies is process wide which has two potential drawbacks. If you want to be able to have different UA strings set for different requests from a WebView that's not really possible with this solution. The other drawback is if you're using out of process WebView, you need to ensure you're calling into UrlMkSetSessionOption in the WebView's process. You'll need to write third party WinRT that calls UrlMkSetSessionOption, create the out of proc WebView, navigate it to some trusted local page, use AddWebAllowedObject or provide that URI WinRT access, and call into your third party WinRT. You'll need to do that for any new WebView process you create.

The second less generally applicable solution is to use NavigateWithHttpRequestMessage and set the User-Agent HTTP header. In this case you get to control the scope of the user agent string changes but has the limitations that not all sub resource downloads will use this user agent string and for navigations you don't initiate you have to manually intercept and re-request being careful to transfer over all POST body state and HTTP headers correctly. That last part is not actually possible for iframes.

PermalinkCommentsuser-agent uwp webview

MSApp.getHtmlPrintDocumentSourceAsync - JavaScript UWP app printing

2017 Oct 11, 5:49

The documentation for printing in JavaScript UWP apps is out of date as it all references MSApp.getHtmlPrintDocumentSource but that method has been replaced by MSApp.getHtmlPrintDocumentSourceAsync since WinPhone 8.1.


Previous to WinPhone 8.1 the WebView's HTML content ran on the UI thread of the app. This is troublesome for rendering arbitrary web content since in the extreme case the JavaScript of some arbitrary web page might just sit in a loop and never return control to your app's UI. With WinPhone 8.1 we added off thread WebView in which the WebView runs HTML content on a separate UI thread.

Off thread WebView required changing our MSApp.getHtmlPrintDocumentSource API which could no longer synchronously produce an HtmlPrintDocumentSource. With WebViews running on their own threads it may take some time for them to generate their print content for the HtmlPrintDocumentSource and we don't want to hang the app's UI thread in the interim. So the MSApp.getHtmlPrintDocumentSource API was replaced with MSApp.getHtmlPrintDocumentSourceAsync which returns a promise the resolved value of which is the eventual HtmlPrintDocumentSource.


However, the usage of the API is otherwise unchanged. So in sample code you see referencing MSApp.getHtmlPrintDocumentSource the sample code is still reasonable but you need to call MSApp.getHtmlPrintDocumentSourceAsync instead and wait for the promise to complete. For example the PrintManager docs has an example implementing a PrintTaskRequested event handler in a JavaScript UWP app.

    function onPrintTaskRequested(printEvent) {    
var printTask = printEvent.request.createPrintTask("Print Sample", function (args) {

Instead we need to obtain a deferral in the event handler so we can asynchronously wait for getHtmlPrintDocumentSourceAsync to complete:

    function onPrintTaskRequested(printEvent) {    
var printTask = printEvent.request.createPrintTask("Print Sample", function (args) {
const deferral = args.getDeferral();
MSApp.getHtmlPrintDocumentSourceAsync(document).then(htmlPrintDocumentSource => {
}, error => {
console.error("Error: " + error.message + " " + error.stack);
PermalinkCommentsjavascript MSApp printing programming uwp webview win10 windows

Tweet from NASA Planetquest

2017 Jan 26, 10:25
See another solar system! These are real images of a 4-planet system ~130 light-years from . Read about it: 

Tweet from David Rousset

2016 Dec 6, 8:45
Creating an extension for all browsers: , , , & : â€¦

Tweet from Jen Gentleman 🌺

2016 Nov 4, 8:39
If you ever see a dialog box in this style & need to record what it said, instead of typing it out, just CTRL+C ➡📋

Tweet from Jen Gentleman 🌺

2016 Oct 8, 2:19
In case you were wondering: Yes, the new address bar that was added to RegEdit supports Alt+D to set keyboard focus 😊

Tweet from Clickbait Robot

2016 Sep 26, 12:53
18 Screwdrivers That Look Like Matt LeBlanc

Tweet from David Risney

2016 Sep 19, 3:04
Playing No Man's Sky collecting resources on an hospitable planet and suddenly notice several creatures approaching. I quickly scan them.

Tweet from Mike Birbiglia

2016 Aug 24, 11:12
When people hack someone's shit you have a responsibility as a decent person to not look at it. You're better than that.

Tweet from Garrett Serack

2016 Aug 18, 2:57
For the record, yes you can run on Linux in Bash on Windows (aka ) /cc @bitcrazed @bradwilson

Tweet from David Risney

2016 Aug 5, 3:20
I've put my WPAD DHCP server Fiddler extension up on GitHub â€¦

WPAD Server Fiddler Extension Source

2016 Aug 5, 3:18

I've put my WPAD Fiddler extension source and the installer on GitHub.

Six years ago I made a WPAD DHCP server Fiddler extension (described previously and previously). The extension runs a WPAD DHCP server telling any clients that connect to connect to the running Fiddler instance. I've finally got around to putting the source on GitHub. I haven't touched it in five or so years so this is either for posterity or education or something.

PermalinkCommentsdhcp fiddler network security wpad

Tweet from Buzz Aldrin

2016 Jul 26, 12:25
47 years ago I submitted my travel voucher reimbursement for my trip to the moon.

Tweet from Rossen Atanassov

2016 Jun 8, 2:59
I recall meetings when we discussed pursuing WebGL... Now we're going open source with it :) â€¦

Tweet from Jen Gentleman

2016 May 13, 3:51
You can use the curser controller just by flicking it 😉 📱

Tweet from Bobak Ferdowsi

2016 Apr 22, 4:40
Hi, you may know me from space, but did you know Earth is my favorite planet? Love it & each other.

Tweet from Kumail Nanjiani

2016 Apr 5, 11:22
Terrified that the will reveal I never beat Dragon Age: Inquisition.

Let's Encrypt Setup

2016 Feb 4, 2:48

2016-Nov-5: Updated post on using Let's Encrypt with

I use for my webhosting for my personal website and I've just finished setting up TLS via Let's Encrypt. The process was slightly more complicated than what you'd like from Let's Encrypt. So for those interested in doing the same on, I've taken the following notes.

The standard Let's Encrypt client requires su/sudo access which is not available on's servers. Additionally NFSN's webserver doesn't have any Let's Encrypt plugins installed. So I used the Let's Encrypt Without Sudo client. I followed the instructions listed on the tool's page with the addition of providing the "--file-based" parameter to

One thing the script doesn't produce is the chain file. But this topic "Let's Encrypt - Quick HOWTO for NSFN" covers how to obtain that:

curl -o domain.chn

Now that you have all the required files, on your NFSN server make the directory /home/protected/ssl and copy your files into it. This is described in the NFSN topic provide certificates to NFSN. After copying the files and setting their permissions as described in the previous link you submit an assistance request. For me it was only 15 minutes later that everything was setup.

After enabling HTTPS I wanted to have all HTTP requests redirect to HTTPS. The normal Apache documentation on how to do this doesn't work on NFSN servers. Instead the NFSN FAQ describes it in "redirect http to https and HSTS". You use the X-Forwarded-Proto instead of the HTTPS variable because of how NFSN's virtual hosting is setup.

RewriteEngine on
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [L,R=301]

Turning on HSTS is as simple as adding the HSTS HTTP header. However, the description in the above link didn't work because my site's NFSN realm isn't on the latest Apache yet. Instead I added the following to my .htaccess. After I'm comfortable with everything working well for a few days I'll start turning up the max-age to the recommended minimum value of 180 days.

Header set Strict-Transport-Security "max-age=3600;" 

Finally, to turn on CSP I started up Fiddler with my CSP Fiddler extension. It allows me to determine the most restrictive CSP rules I could apply and still have all resources on my page load. From there I found and removed inline script and some content loaded via http and otherwise continued tweaking my site and CSP rules.

After I was done I checked out my site on SSL Lab's SSL Test to see what I might have done wrong or needed improving. The first time I went through these steps I hadn't included the chain file which the SSL Test told me about. I was able to add that file to the same files I had already previously generated from the Let's Encrypt client and do another NFSN assistance request and 15 minutes later the SSL Test had upgraded me from 'B' to 'A'.

PermalinkCommentscertificate csp hsts https lets-encrypt

Retweet of windowsblog

2015 Dec 4, 5:23
Microsoft Edge’s JavaScript engine to go open-source 

Tweet from David_Risney

2015 Oct 23, 3:55
Crowd sourced morality on automated cars handling collisions: â€¦ 3 laws is thin API over Amzn Mechanical Turk service.
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