Hello user6241929,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
You will want to use the Redirect URL to send the authorization code from the Authorization Request URL back to your Application in order to exchange it for your initial token set.
Example Authorization Request URL https://v3.developer.constantcontact.com/api_guide/scopes.html#example-authorization-request-url
Get the Token from the Redirect URL https://v3.developer.constantcontact.com/api_guide/auth_overview.html#get-the-token-from-the-redirect-url
There is no way to bypass the Authorization Request screen (which is only accessible via browser), but you should only need to authorize an account once. Once you go through the V3 API OAuth2.0 Server Flow in order to get an access token and refresh token for your key, you can use access tokens to make requests using the V3 API, and refresh tokens to obtain new access tokens without any user input. This ensures that your users only need to authenticate once.
Please have a look and let us know if you have any other questions!
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