I cannot log in to my Flickr account using my Google credentials anymore. A little history on that. In late 2010, Flickr announced that they enabled single sign-on via OpenID and allowed users to log in via their Google accounts:

We’re introducing OpenID on Flickr, a service that makes it faster and easier to sign-up for new accounts by letting you use one identity across multiple websites. So starting today, you’ll be able to use a Google account to sign-up for a new Flickr account. We’re pleased to announce Google as our first partner, but stay tuned as we continue to add even more in the future!

Over time, Yahoo allowed many of their services to be used with Google and Facebook identities. I myself used Flickr via my Google account. Just recently, however, when I logged in to Flickr via Google, Yahoo forced me to create a Yahoo account in order to proceed using my Flickr profile. Indeed, in March 2014, Yahoo released to the press that they will gradually stop supporting single sign-on for their services:

The sign-in buttons for Facebook and Google will eventually be removed from all Yahoo properties, the Yahoo spokeswoman, though she declined to provide a timeframe.

Why is that?

“Yahoo is continually working on improving the user experience,” the company said in a statement, noting that the new process “will allow us to offer the best personalized experience to everyone”.

I do not agree. I could have created a real Yahoo account whenever I wanted to, and likewise was always able to decide by myself how to achieve best user experience. Of Yahoo’s services I am only using Flickr, so I really do/did not need a Yahoo ID. Stating the obvious, Yahoo wants to bind people to their services as tight as possible, sell ads as valuable as possible, and collect statistics with as much detail as possible. In order to achieve this, full control over the user accounts is advantageous. Clearly, we can not log in to Facebook or Google using just our Yahoo accounts.

This technical change is part of a larger change in strategy:

In eliminating the Facebook and Google sign-in features, Mayer, a former Google executive, is effectively reversing a strategy that Yahoo adopted in 2010 and 2011 under then CEO Carol Bartz.

I am a bit pissed of by that. However, I can imagine that in the long term all this was a neat plan of Yahoo: dramatically simplify using Yahoo services for a couple of years (via single sign-on) and then, when people depend on certain Yahoo services, enforce them to create real accounts. This might pay off.