This post was most recently updated on October 26th, 2018.
Every now and then, something like half of Microsoft’s websites will suddenly stop working – this applies to Azure Portal, SharePoint Online sites, MSDN forums and probably a thousand of other sites. The error is most of the time something like this:
Bad Request - Request Too Long HTTP Error 400. The size of the request headers is too long.
Or like shown below:
This effectively blocks you from accessing the site. Most typically, I’ve encountered this on MSDN forums or Azure Portal – I’ve just faced a very blunt, unfriendly and quite useless error message, like above. This applies even to Microsoft’s services, that don’t seem to require logging in – but actually do so, in the background. Annoying!
Yet once again, the solution is almost stupidly simple.
This has left me scratching my head a few times – why can’t I access SharePoint Online anymore? Why do I get a Bad Request error when accessing MSDN forums? What’s this HTTP Error 400 when opening Azure Portal? Yeah, it is a bit baffling, isn’t it?
Most of the time, weirdly enough, it wasn’t your fault though. There’s something amiss with the authentication configuration – and there’s a workaround.
This seems to be simply a cookie mismatch error of sorts, and this error (in a couple of different forms, I guess) has existed on Microsoft’s different sites for quite a few years already. I’m guessing it’s caused by using multiple different accounts for authenticating against different Microsoft’s sites and services, and some of the cookies being leftover from earlier sessions and sites just trying different implicit logging in maneuvers – but failing.
In the end, all of this is just guesswork. The more important part is, that it’s easy to fix!
Solution: Remove all cookies for that particular domain
Since it’s the authentication cookie, that has somehow gone haywire, we’ll need to get rid of it. The simple fix is just to change browser, to clear the cache of your browser, but if you just want to get rid of the offending cookie and save everything else, here’s what to do!
Click on the site info area in Chrome’s Omnibox (that’s the name of the URL text box in Chrome!), and depending on your Chrome version, either click on “X in use” under “Cookies”, or just click on “Cookies (x in use)”.
This should open a new window, where you can see different domains that have set cookies for this site. Now, click “Remove” while you’ve selected the domain you were logging in for (or if “login.microsoftonline.com” exists, you can select it, too).
After removing the cookies, you should be able to log in successfully when refreshing the page! On some pages, such as MSDN forums, the log-in action might be implicit (it happens automatically in the background). Hence you won’t be ever asked any questions or asked to do any logging in actions.
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