val request = Request.Builder()
            .url("http://publicobject.com/secrets/hellosecret.txt")
            .build()
      }
    ```

    To avoid making many retries when authentication isn't working, you can return null to give up. For example, you may want to skip the retry when these exact credentials have already been attempted:

    ```kotlin
    if (credential == response.request.header("Authorization")) {

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