@hungChun We understand you would like more samples of how to obtain token's; specifically tokens on Android.
We have gone ahead and created the document feedback request and assigned it to the document author since this requires a larger rewrite of the document.
In the future, feel free to go ahead and create the document feedback request by following the steps to provide feedback at the bottom of the document(s).
You can track the request here. Please let us know if you have any questions or concerns.