Hello LauraG70,
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.
Our current V3 API uses OAuth2.0, which is the current industry-standard for authorization. It’s more secure than previous versions and does a much better job of keeping your Constant Contact account data safe. When you give their integration permission to access your account, it will show you exactly which permissions the integration is requesting to be granted (rather than just granting all permissions). V3 also uses tokens that are continuously refreshed to keep the connection encrypted and secure.
The request for V3 application code samples is currently under review. However, we're currently still adding endpoints and capabilities to the V3 API, and do not plan to publish official sample apps until that process is complete. Your feedback and experience with this request is essential to improving our product, so thank you for reaching out to us regarding this matter.
In the meantime, here are the example calls that are currently available for V3:
V3 Code Samples:
https://v3.developer.constantcontact.com/api_guide/tag_code_samples.html
Additionally, you can utilize our API Reference tester to test out the functionality of our available endpoints to see how they will work once programmed within your application:
https://v3.developer.constantcontact.com/api_reference/index.html
For additional reference, here is the link to a sample that was created/shared on our Developer Forum by a 3rd party developer (NOT created or supported by Constant Contact) for V3 using PHP:
https://community.constantcontact.com/t5/Developer-Support-ask-questions/PHP-V3-Library-now-updated-to-new-OAuth2-endpoints-and-PKCE/td-p/383773
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