curl -i -X POST "https://api.box.com/oauth2/token" \
     -H "content-type: application/x-www-form-urlencoded" \
     -d "client_id=[CLIENT_ID]" \
     -d "client_secret=[CLIENT_SECRET]" \
     -d "refresh_token=[REFRESH_TOKEN]" \
     -d "grant_type=refresh_token"

auth.refresh_token()

await auth.refreshToken();

try await auth.refreshToken();

auth.refreshToken();

await auth.RefreshTokenAsync();

{
  "access_token": "c3FIOG9vSGV4VHo4QzAyg5T1JvNnJoZ3ExaVNyQWw6WjRsanRKZG5lQk9qUE1BVQ",
  "expires_in": 3600,
  "token_type": "bearer",
  "restricted_to": [
    {
      "scope": "item_download",
      "object": {
        "id": "12345",
        "type": "folder",
        "etag": "1",
        "sequence_id": "3",
        "name": "Contracts"
      }
    }
  ],
  "refresh_token": "c3FIOG9vSGV4VHo4QzAyg5T1JvNnJoZ3ExaVNyQWw6WjRsanRKZG5lQk9qUE1BVQ",
  "issued_token_type": "urn:ietf:params:oauth:token-type:access_token"
}

{
  "error": "invalid_client",
  "error_description": "The client credentials are not valid"
}

{
  "error": "invalid_client",
  "error_description": "The client credentials are not valid"
}