I personally used the OFA Facebook application and the intent is incredibly different. Notably, the folks who authorized the OFA application knew that the data about their friends was being collected. Because that was entirely the point! We were using it to send out requests to our friends to persuade to them to vote/register to vote.

If you'd like a more in-depth explanation, I found this post by the former Chief Scientist of Obama For America campaign (2012) that goes into the key differences between how the data was collected & used compared to Cambridge Analytica: https://medium.com/@rayid/why-what-cambridge-analytica-did-w...