Hello @PREPARE79,
Thank you for reaching out to Constant Contact's API Support.
Our API currently has a single method of authentication with oAuth2 and that is with generating an Access Token. If this process is only going to be seen by you then you can use https://localhost as the redirect URI which will direct you to a generic website.
We are exploring other options to our authentication, but at this time we do not have an eta on those options.
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