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first draft of whats wrong with the browseri api

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+title: What's Wrong With the BrowserID API?
+This post explores problems with the existing BrowserID API, specifically
+there are features that simply cannot be implemented with the current API.
+I'll talk about four important features that would require a change to
+the API, and discuss the precise ways in which it would need to change.
+## The Current API
+The current API for BrowserID is simple and delicious, consisting of
+two functions:
+ // attempt to get an assertion, possibly causing the user
+ // to be prompted. Options include:
+ // silent: boolean indicating whether the user should be
+ // prompted. when false, an assertion will only
+ // be returned if the user has chosen to "stay signed
+ // into this site" in a previous interaction.
+ // requiredEmail: When provided contains an email that the
+ // user must use.
+ // allowPersistent: give the user the option to "stay signed
+ // into this site".
+ //
+<callback>, [options]);
+ // the user has indicated with actions in content that they
+ // wish to be logged out of this site, so if they've previously
+ // indicated they wish to "stay signed in", that preference should
+ // be reverted.
+An important subtlety is that there are actually two ways that one could
+apply the API:
+ * The simple usage: Call `.get` when the user clicks a button, and
+ after validating an assertion, set a cookie. Do nothing else.
+ * The complex usage: Call `.get` with `silent` set at page load when
+ the user is not logged in. Call `.get` with `allowPersistent` set
+ when the user clicks a sign in button. Finally, invoke `.logout`
+ when the user indicates (with a click) that they want to logout of
+ the site.
+The former usage is extremely simple to explain and apply. The latter,
+however actually moves more control of session length into BrowserID
+which makes some valuable features possible.
+The problems with the current API are twofold:
+ 1. the simple usage affords no way for a site to be informed that a
+ user is already signed in, which prevents many UX optimizations,
+ and user features.
+ 2. Because two paths exist, we are constrained by the simple application.
+ For instance, if we sign the user in automatically as part of the
+ verification process (when the site using BrowserID isn't loaded),
+ there's no way to tell the site later that the user is already
+ logged in and give them an assertion.
+## BrowserID's Missing Features
+What features would we like to build into BrowserID and why do they
+### Sign-out
+Currently the only way a user has of meaningfully "Signing out of all
+sites" is to tell their browser to "Clear recent history" or to
+"Delete cookies and other site and plug-in data". In my opinion,
+neither of the two user facing phrases clearly indicate the result in
+the way that a user can understand. Further, these actions are both
+meaningless and insufficiently granular: if the user wishes to "sign
+out everywhere" but not "remove all of my site preferences and data",
+they cannot do this.
+If sites don't more frequently ask BrowserID "is the user signed in",
+then we have no way of offering the user features like selective or
+global sign out of their browser.
+### A Streamlined UX
+The weakest point of BrowserID's UX is when the user is required to go
+check their email and navigate back to the site they're signing into.
+It is too hard to get from the link in your email back to the site
+that you started from in a signed in state. Currently we require the
+user to manually locate the tab where they initiated the action.
+We've found via user testing that we can improve percieved experience
+for 8/9 users by having the link in email take the user directly back
+to the site that they were visiting
+In order to make this streamlined UX work, the page using BrowserID must
+be able to detect that the user is logged in without prompting them.
+### Keep Me Signed In, For Real.
+Depending on the security concerns of a given site, the period which you
+remain logged in can vary wildly. This is a typical tradeoff between
+security and usability, where a shorter authentication period can reduce
+user risk, but also requires the user to type their password more often.
+In addition to the assessment of the site, optimal authentication
+duration should consider other factors related to the user:
+ * Is the user on a computer that is not her own?
+ * Does the user share her computer with others?
+ * Has the user recently (or ever) signed in with this computer?
+ * If the user is savvy, have they expressed an explicit desire about how long they wish to be signed in?
+ * Has the user expressed a desire regarding duration specifically for this site?
+The work of considering all of these factors and building a perfect UX
+is hard. It's also something that UX folks at mozilla are attacking
+head on. This work has the potential to further reduce the amount of work
+that sites must do while improving their security and usability.
+A prerequisite for better authentication duration is for the user (via
+BrowserID or their browser), to have more control over session duration.
+If sites were to decrease session (cookie) duration and get "silent
+assertions" from BrowserID more frequently, then the requisite hooks would
+be in place to implement the features discussed above: users will be able to
+feel like they're "signed in" for long periods of time, but with a simple
+and intuitive action they'll be able to prevent unwanted access to their
+### Better Browser Integration
+A final area where any API that allows BrowserID to tell the page that
+the user has signed in or out is beneficial, is that it makes it possible
+for the browser itself to display such buttons in browser chrome, which
+can improve security (better phishing countermeasures) and usability
+(identical experience across sites).
+## The Requirements
+The four features above distill into several concrete requirements that
+we can work from:
+ 1. BrowserID (or the Browser) must be able to send the page an event
+ at any time indicating that the user is logged out
+ 2. BrowserID (or the Browser) must be able to send the page an event
+ indicating that the user is logged in
+ 3. There should only be a single patterned way to use BrowserID that
+ lets sites support central sign-out and streamlined UX without
+ additional work. (Not a "simple" and a "complex" path).
+## The Problem
+These changes, making it that the way you implement BrowserID supports
+these features automatically, necessarily makes the implementation of
+BrowserID on your site more complex. To make this clear, let's contrast
+informal flow diagrams of present API (in its simplest form), with a
+chart of what we would need to migrate to.
+### How We Implement BrowserID Today
+The following diagram represents what how you implement the "simple API"
+of today on your site:
+ <center>
+ <a href="/posts/i/bid_api_today.jpg">![applying BrowserID today](/posts/i/bid_api_today.png)</a>
+ </center>
+In this view, the notion of an "authentication session" is completely up
+to the site to manage. If there is a cookie, for example, set by the
+site that indicates that the user is logged in, that is always up to date.
+Further, the site makes exactly one javascript call into BrowserID,
+`` and that call is made at the time the user clicks on
+a "sign in with BrowserID" button.
+### How We Might Change Things
+What might things look like when a page implements a future version of
+BrowserID that supports the desired features discussed above?
+ <center>
+ ![applying BrowserID tomorrow](/posts/i/bid_api_tomorrow.png)
+ </center>
+The key difference in this diagram, is that at the time a request is
+issued to the server, the presence of a session cookie is insufficient
+to know if the user is logged in. Each page sent must double check
+that state to see if the user has signed in or out out of band.
+Further, something that's not represented in this digram, is that sites
+implementing BrowserID would have to subscribe to some sort of event,
+to check if the user signs in or out at some point after the page has loaded,
+either via browser chrome or otherwise out of band.
+## Challenges
+There are a pile of issues to consider in moving to a more complex API
+for BrowserID, not the least of which is first run developer experience.
+The harder it is to apply BrowserID, the fewer people that will apply
+it. On the other hand, the features above are compelling and make
+rich user controls and a better experience possible. So let's explore
+the different issues that should be considered when making this change.
+#### Traditional Web Sites
+A common trend in web development is single page web applications. Pages
+that serve a pile of resources at initial load and then provide most
+of their functionality using client side javascript, sometimes using
+features like [pushState][] to preserve user expectations.
+ [pushState]:
+This model is interesting, but not all sites work like this. How specifically
+would a more traditional web application consisting of distinct pages apply
+this new BrowserID in the new model?
+A typical pattern in a standard web application may be to have a single
+page where users are directed to logout - `/logout`, and another where
+they would be sent to sign in `/signin`. For pages of this type, they
+could defer to their traditional session mechanism to determine if a user
+was authenticated at the time they receive a page request.
+If the user *is* authenticated, they would serve javascript that would
+register with `` in some fashion to be notified when a user
+logs out. Upon detection of logout they would redirect the user to
+the specified page from javascript.
+The reverse is true if a user is signed out, javascript would have to be
+served with pages where the user is signed out that would detect and
+redirect to a sign in page when it's detected that the user is "signed in"
+with BrowserID, despite the absence of a site controlled session.
+Some UX challenges that arises is clumsy page reload - how
+common will it be that a page is loaded, the user sees the content
+(customized for them), and then almost immediately that page is torn
+down, and another where they're logged out is rendered?
+#### Up Front Resource Costs
+Until BrowserID is implemented natively, javascript resources are required
+to generate assertions. These resources are about 80k gzipped and minified,
+and are spread over four or five files.
+In the present way that BrowserID works, these resources are lazily served
+at the time that a user authenticates (actually clicks the sign in button
+and sees the BrowserID dialog). In the new model, we would need to add
+an iframe to the DOM and load resources into that iframe at every page
+This change may be distasteful to some users and we must figure out a
+way to minimize the cost. If the total cost were two new files whose
+aggregate gzipped and minified size were about 10k, would potential adopters
+of BrowserID still be off-put?
+#### Assertion Generation Cost
+[Some alluringly simple API proposals][] for this new model suggest that
+we might implement this new model by simply firing a 'login' event at every
+page load where a user is signed in, having the payload of that event
+include an assertion.
+The issues that exist with this proposal include resource loading above,
+you would require the full 80k on every page-load, in addition to compute
+costs of generating an assertion.
+For multi-page web applications, this added activity at page load time
+might contribute to a sluggish website feel.
+A way around this problem would be to build the new API in a manner that
+performs a low cost operation to determine if the login state of the
+user is other than as perceived by the site, and only if required (upon
+further action by the site) do the work to generate an assertion.
+#### Third Party Cookies Disabled
+Many awesome browsers offer an option to users to disable third party cookies,
+that is cookies bound for domains other than that of the current webpage.
+Often privacy conscious users opt to disable third party cookies as they are
+most frequently used for user tracking and advertising.
+Because of the way that we would have to implement the new API to support
+these features, this browser option will limit the success of user transparent
+assertion generation, and would require users with this option enabled
+to interact with the BrowserID dialog much more frequently.
+Native browser implementations would solve this problem, and as the failure
+mode here does not block users from using their sites, this is not
+a huge issue.
+#### Required Email
+A feature exists in BrowserID today to allow a website to specify the email
+address that it wants a user to verify. This feature is applicable in
+scenarios where the user has shared an email address with a site out of band,
+and the site wishes to use BrowserID to confirm that the user is actually
+in control of the address.
+For this feature to function properly, one of two things is required:
+ * the site must be able to easily check to see if the address confirmed
+ by an assertion is the one it wants
+ * OR, the site must be able to tell BrowserID which specific email
+ it wants before any assertions are issued.
+The complexity added by a new API with respect to this feature, is that
+the API must have a convenient way to represent its constraints on the valid
+email address before BrowserID does any processing. Presently, this
+constraint is just an option to the `.get` call. Alternately, we might
+choose to make it simpler for sites to check the email address on the
+client, before verification.
+This is not an intractable problem, but it will require careful API design.
+#### Primary Email Providers
+Finally, in the event that your email address is associated with a provider
+who has implemented BrowserID support, we must consider how this affects
+your session duration. Shall we say you are only logged into a site if
+you are also authenticated to your provider?
+This issue is more of a UX challenge, and many possibilities are opened
+by increasing the scope of the BrowserID API.
+## tl;dr;
+There are many interesting features that we could build into
+BrowserID. These features have the potential to make things safer and
+easier for users on sites that support BrowserID. To make them
+possible, we would need to make the BrowserID API more complicated to
+apply, which will likely hurt adoption.
+Previously we've tried to have it both ways, to preserve the dead
+simple API that developers have praised - but to offer a more complex
+api that makes a better UX and important user facing features
+possible. This route is no longer useful, as we get the cost (we
+confuse people) without the benefit: the ability to improve UX and
+user control.
+Next steps? Given the issues above, let's find the best possible API.
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BIN posts/i/bid_api_tomorrow.png
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