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title: Authenticate API Calls with Salesforce Scheduler APIs
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# Authenticate API Calls with Salesforce Scheduler APIs

Use OAuth—the most secure SOAP and REST API call authentication method—to get an access token.

**note:** You can't modify an existing appointment via a guest user profile. You can use an integration user who has permissions to read and update only the required objects.

If you are working in a Salesforce organization that has a Developer Edition, an Enterprise Edition, or above, verify that you have the API Enabled permission. This permission is enabled by default. This permission allows you to access any Salesforce API.