CAST Extend has a built in API that can be accessed in a manner of ways. API documentation exists and is provided by Swagger. This documentation is interactive and you can test requests directly. The API documentation is accessible via the following URL:
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Using the API interactively
Expand the specific request using the blue section in the top left:
Click Try it out:
Some actions require authorization - these are marked with a padlock. Click the padlock to choose an authorization method and enter credentials/API key:
You can obtain an API key when logged into CAST Extend in your user profile.