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In the movie Ferris Bueller’s Day Off, a valet attendant takes a fully restored 1961 Ferrari out for a joyride. How do you prevent the same thing from happening to your brand-new Mustang? Some cars now come with special keys that allow the owner to provide limited authorization to valet attendants (or kids!) and prevent activities such as opening the trunk and driving at excessive speeds.
OAuth was created to solve the same core issue online.
When Google first released the Google Calendar API, it provided the ability for application developers to read and manipulate a user’s Google Calendar. However, the only way for a user to provide delegated access was to give the application his or her account username and password, which the application would then use with Google’s proprietary ClientLogin protocol.