How do you use a bearer URL?

In “Towards a standard for bearer token URLs”, I described a URL scheme that can be safely used to incorporate a bearer token (such as an OAuth access token) into a URL. That blog post concentrated on the technical details of how that would work and the security properties of the scheme. But as Tim Dierks commented on Twitter, it’s not necessarily obvious to people how you’d actually use this in practice. Who creates these URLs? How are they used and shared? In this follow-up post I’ll attempt to answer that question with a few examples of how bearer URLs could be used in practice.

The bearer URL scheme
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Towards a standard for bearer token URLs

In XSS doesn’t have to be Game Over, and earlier when discussing Can you ever (safely) include credentials in a URL?, I raised the possibility of standardising a new URL scheme that safely allows encoding a bearer token into a URL. This makes it more convenient to use lots of very fine-grained tokens rather than one token/cookie that grants access to everything, which improves security. It also makes it much easier to securely share access to individual resources, improving usability. In this post I’ll outline what such a new URL scheme would look like and the security advantages it provides over existing web authentication mechanisms. As browser vendors restrict the use of cookies, I believe there is a need for a secure replacement, and that bearer URLs are a good candidate.

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XSS doesn’t have to be game over

A message I’m very used to seeing – but does XSS have to mean game over for web security?

There’s a persistent belief among web security people that cross-site scripting (XSS) is a “game over” event for defence: there is no effective way to recover if an attacker can inject code into your site. Brian Campbell refers to this as “XSS Nihilism”, which is a great description. But is this bleak assessment actually true? For the most part yes, but in this post I want to talk about a faint glimmer on the horizon that might just be a ray of sunshine after all.

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API Security in Action is published!

I wasn’t expecting it so quickly, so it caught me a little off guard, but API Security in Action is now finally published. PDF copies are available now, with printed copies shipping by the end of the month. Kindle/ePub take a little bit longer but should be out in a few weeks time.

My own print copies will take a few weeks to ship to the UK, and I can’t wait to finally hold it in my hands. That’s a brighter ending to 2020.

At some point I’ll try and collect some thoughts about the process of writing it and my feelings with the finished product. But tonight I’ll settle for a glass (or two) of a nice red. Cheers!

Can you ever (safely) include credentials in a URL?

Update: an updated version of the ideas in this blog post appears in chapter 9 of my book. You may also like my proposal: Towards a standard for bearer token URLs.

URLs are a cornerstone of the web, and are the basic means by which content and resources are shared and disseminated. People copy and paste URLs into Slack or WhatsApp to share interesting links. Google crawls the web, discovering and indexing such links. But what happens when the page you want to link is not public and requires credentials in order to view or interact with it? Suddenly a URL is no longer sufficient, unless the recipient happens to already have credentials. Sometimes they do, and everything is fine, but often they do not. If we really do want to give them access, the problem becomes how to securely pass along some credentials with the URL so that they can access the page we have linked.

A commonly desired approach to this problem is to encode the credentials into the URL itself. While convenient, this solution is fraught with dangers and frequently results in credentials being exposed in insecure contexts. In this article, we’ll look at various ways to accomplish this, the ways that things can go wrong, and conclude with a set of guidelines for cases where this can be made secure, and actually improve security overall.

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