Tuesday 29 March 2011

The irony and the tragedy of OAuth scopes

Overly broad permissions

I was taking a look at my PeerIndex profile when I got the above screen. I was surprised since the button I clicked said "sign in with Twitter" and didn't mention anything about updating my data. I did a little digging and it seems that I'm not the only one who has this reaction.

In my case it was especially ironic since one of the things that I've been trying to do with the Buzz APIs is encourage developers to ask for the minimum set of permissions that they need.

The idea is that an app which is just going to use its access to your account to gather metrics shouldn't also be able to post messages on your behalf. That's why we expose 3 different scopes. These are read-only, read-write and a special scope for photos because those tend to be especially sensitive.

However developers will often just ask for the maximum set of scopes in order to give themselves the freedom to implement new features later on without having to ask the user to re-authorise them. They do this because it's easier for them and because they believe it results in a better user experience since the user isn't constantly being asked to give permission.

Unfortunately what many developers don't notice are the users who get to the authorisation screen and then close the tab because they don't understand why your app needs write-access to their account. The point is that asking for overly broad permissions, just like the password anti-pattern, repels users.

In the case of the Twitter API the problem seems to be that any HTTP POST API call is considered a write and so services like PeerIndex end up needing to ask for read-write access even though they're well-behaved.

The tragedy is that all parties are trying to create the best possible user and developer experience (by avoiding complicating the user interfaces with lots of options and removing the need to constantly ask the user for new permissions) but the end result is bad for all concerned.

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