I’m reading the protocol workflow of OAuth – http://hueniverse.com/oauth/guide/workflow/
I understand the need for access credentials in OAuth since they guarantee that the user has given access to his resource, however what is the purpose of temporary credentials? They are apparently necessary to redirect the user to the server’s login page, but why? Would the service be less secure without them?
That temporary credentials (read request Tokens) are required to ensure that the request for access tokens is coming from an authorized client.