How does OAuth 2.0 actually solve the problem?
In order to see how OAuth 2.0 solves this problem of sharing resources, let's look at how this problem was solved before OAuth 2.0 was created.
Without OAuth 2.0 – GoodApp wants to suggest contacts by looking at your Facebook friends
Imagine that you have just signed up for the service GoodApp. As a new user, you don't have any contacts. GoodApp wants to suggest contacts for you to add by looking at your Facebook friends. If any of your Facebook friends are on GoodApp, it will suggest that you add them.
Before the creation of OAuth 2.0, this was solved in a very insecure way. GoodApp would ask you for your username and password for Facebook. GoodApp would then log into Facebook on your behalf to get ...