Get the accessToken of a client with Javascript

Hi,

I would like to get the accessToken of a client with Javascript if possible. 

I have his username, his password and the link for an emebbed report.

this is my link : https://app.powerbi.com/groups/me/reports/my-report-id?ctid=my-client-id

So with all these informations, can i get the access token so i can embed the report on my own ? 

I tried to use the javascript's code of "v-ljerr-msft" in this thread (https://community.powerbi.com/t5/Developer/get-Access-token-using-js/m-p/350294#M10396) but it doesn't work with my clientId. 

I get this error :