Hello NateP57,
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.
We now offer the Device authorization flow for the V3 API which is intended for applications which run on devices that are input constrained. This authorization flow does not require the use of redirect URLs, callbacks, or the client secret. I’m including our documentation on this flow below.
OAuth2 Device Flow:
https://developer.constantcontact.com/api_guide/device_flow.html
Please have a look and let us know if you have any other questions!
Regards,
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