Having problems to find the Power BI AccessToken

Hello everyone,

I am trying to generate the Acess Token for my report.

I am trying to do so by following this tutorial: https://msdn.microsoft.com/library/mt784614.aspx

So in the tutorial, it says to make a post request to this link: https://api.powerbi.com/v1.0/myorg/groups/{group_Id}/reports/{report_id}/GenerateToken

I understand what group_id and report id is, but in the Header I am supose to give the Power BI access token.

Header
Content-Type: application/json; charset=utf-8
Authorization: Bearer eyJ0eX ... FWSXfwtQ

The Authorization header is the Power BI AccessToken.

Where can I find this Power BI AccessToken?

Thank you very much,

Henrique.