Hello @RohitS849,   Thank you for reaching out to Constant Contact's API Support.   We are looking in to a server to server option, but at this time this is the only authentication option available. I'm not sure why you say that this is not a one time step. Once you get the Access/Refresh Token the first time you will not need a human to login and click the Allow button again. You will need to refresh the tokens, but that process can be automated without human interaction. ... View more