20. Persona, OpenID, SAML, WebID, and Webfinger
Virtualization of sessions
A sound system can usually be operated by whoever has physical access to it. This is a very simple system which humans understand well. If you want only the DJ to play music, then you just construct a physical DJ booth, and people naturally sense that they're not allowed to enter it, or to lean over the table from the other side. For gaming consoles and PCs this can also still work. Laptops usually have a password-protected lock screen, which means a thief of the physical object can't access the data on there. And shared computers will have multiple user accounts, to shield users from each other, and restrict admin (root) access to the device's configuration.
This means that a single device often already provides a concept of accounts and sessions: a session is one user currently using the device, and during such a session, the user has unemcumbered access both to the device's capabilities, and to that user's own data. A session is started by providing some sort of account credentials, and exists for a finite contiguous timespan.
When you connect computers with each other into a network, all of this becomes immensely more complicated. First of all, physical access is no longer needed to open a session on a device, and largely because of this, there can be multiple sessions active simultaneously on the same device.
Most networking protocols provide a way to establish such remote sessions. This is sufficient if a user habitually uses the same client device to log in to the same server device. But the virtualization and decentralization of applications and services we use in everyday life introduces two problems. First, we need to log in to many different servers, and managing all those credentials becomes a complicated task.
Client-side master sessions
A simple solution for this is to store a "master session" on the client device, which can give access to an unlimited number of remote server sessions.
WebID-TLS is based on this idea: you create an asymmetric key pair inside your browser profile on your favorite client device, and use that to establish remote sessions at servers that support WebID-TLS. The same setup is often used for ssh, git, and other protocols that support asymmetric cryptography.
But this also brings us to the second problem: we increasingly want to log in from many different clients. You can link your account on a client device to your remote accounts on thirty different services, but then you can access your remote accounts only from that one client device.
A first step to solving this is to "sync" devices with each other. Browser synchronizers like Firefox Sync allow you to synchronize your laptop's master session between for instance your laptop and your smartphone. I'm not sure whether any of them also sync your client-side SSL certificates, but let's imagine they do. For some people this is a great solution, because you can use multiple client devices, and always have seamless access to all your server-side accounts and sessions. Also, having your master session synchronized over multiple client devices, automatically acts as a backup of all these credentials.
But whether or not this is a good enough way to organize your decentralized user accounts, heavily depends on your usage patterns. A lot of people (for instance the kids at village internet cafes in rural Bali) don't own their own client device. They just use a random public computer when they need to access any of their server-side accounts. Also, many people want to be able to use a random client device to access their stuff under special circumstances, for instance, when travelling. This is where the client-side master session breaks down as a viable solution.
If you want to have less different credentials for many servers where you have accounts, but you don't want to rely on any particular client device or set of client devices, then federated login is another possible solution. For instance, if you have your own server, then you can create your master session on there, and use it as a jump box, a server you can reach from any client device, and from there have your access to all the other servers you may need to open sessions on.
Application providers could provide free jump box functionality to all their users, and that way they would effectively be "federated": you promote one your remote accounts to become the master account from which all your other accounts are reachable.
The server that is in the middle, in the jump box role, is then seen to provide "identity": you log in to control an imaginary puppet on that server, and that puppet (your online identity) then logs into the eventual session you want to use. Through clever tricks it's even possible to use the intermediate server only to establish trust during the session setup between the client and the application server, and not throughout the duration of the remote session. This is why such a federated jump box service is also known as an identity provider.
If all servers where you want to establish remote sessions support OpenID, then you can promote one of these servers by making it your identity provider, and use the trust between these servers to log in with that identity.
Unfortunately many servers do not provide OpenID, when they do they often only accept a certain whitelist of identity providers, and the process of using OpenID to log in on a website is often confusing and cumbersome, which in turn has hindered adoption.
Native Persona with a primary identity provider is better than OpenID in its user interface, because it uses the browser chrome to transport trust between two open browser tabs. In case none of your remote accounts are Persona primaries, there is also a centralized secondary identity provider which allows you to create an identity account, bootstrapped from your email account.
In fact, the way Persona is presented to the user, the assumption is that you will use your main email address as your online identity. This makes sense because a lot of online services provide email-based password resets anyway, which already turns your primary email adress into your de facto identity provider.
Within enterprise intranets, services are often linked together using SAML, which is a well-established framework for federated login, but which was designed for closed ecosystems instead of open ones, so that makes it more suitable for use on intranets than for use on the internet as a whole.
In the IndieWeb community, IndieAuth is a popular way to allow polyglot federated login, using various social network sites for the identity plumbing.
Own your identity
In practice, at the time of writing, Facebook Connect is probably the most popular cross-origin login scheme. It is proprietary and centralized, and together with the Facebook Like button, it gives Facebook mighty powers over the web as a whole. Some other application providers provide comparable niche schemes, like logging in with Twitter and logging in with Github. Many relying parties seem to have replaced their "log in with OpenID" button with a "log in with Google" button.
This is a big problem, of course. As I already emphasized in previous episodes, your online identity should derive directly from a DNS domain name that you own.
This also allows you to host your own public profile, with some basic public information about yourself, as a web page. At the same time you can then use Webfinger to provide a machine-readable version of that same public profile page. And of course, you should add email hosting to your domain name, and become your own OpenID provider, as well as your own Persona provider, on your own DNS domain name.
That is the only proper way to deal with identity on the web: don't outsource your identity to Facebook or Google, own it yourself!
And the ultimate solution...: don't log in!
All this talk about logging in to hosted sessions, disgusting! ;) Our goal with remoteStorage, Sockethub, and unhosted web apps, is of course to decentralize applications away from specific application servers, meaning you don't have to log in to an application-specific server at all.
When you use an unhosted web app, you do not log in to the application. Instead you connect the application, which runs client-side, to your own per-user server. This completely eradicates hosted applications, and with it the problem of logging in to many different hosted applications.
The word "identity" is often used in two different ways: once as the address where other users can find you, and once when talking about the identity with which you log in to a service. For the first one you can register your own DNS domain name, as your Indie Web presence, or get an account at a shared domain name. You can then host a human-readable public profile page on there, as well as a machine-readable public webfinger profile, or keep it "stealthy", and for instance only give out your email address to your closest friends. Whether public or not, this is your identity towards other users.
The second one, identity for login, is not a problem in unhosted applications: there are no per-application sessions, only per-user sessions. Still, I wanted to dedicate an episode to it, since it's an important background topic, and we often get the question "how do unhosted web apps interact with Persona". So now you know. The answer is: they don't have the problem that Persona solves. :)
Next: Client-side sessions, origins, browser tabs, and WebIntents