How to retrieve all 3rd party apps in Google workspace / Google admin SDK using API?

The Google Admin SDK doesn't have a method that only retrieves the 3rd party connected apps, but you could use the method activities.list using applicationName=token once you have the Oauth tokens you can filter out third party applications based on the product_bucket .

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Edit:

You could try this example on App Script, that will display the token authorized for your users in the organization.

function myFunction() {
  let request = {
    "eventName": "authorize"
  };
  let appsList = [];
  let response = AdminDirectory.Activities.list("all", "token", request);
  for(let i=0; i< response.items.length; i++)
  {
    if(appsList.includes(response.items[i].events[0].parameters[1].value)==false)
    {
      appsList.push(response.items[i].events[0].parameters[1].value);
    }
  }
  Logger.log(appsList);
}

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Before you run the code remember to add the advance service Admin SDK

Then, change the Version to Reports_v1

References:

• Method Activities.list
• OAuth Token Audit Activity Events