Thank you for your answer.
Carefully? Yes :-)
Well, the JS API is not what I'm struggling with. It's the last thing to check on my todo. And I don't want to create a .Net project, but a Rails one. The basic process are the same, I understand that.
Here's a bunch of questions, thank you for your expertise & advices :
#1
Do I need to register an application for Power BI with https://dev.powerbi.com/apps?type=web ?
(I've already done that)
#2
Do I need to create an ActiveDirectory (and a Azure User) ? Then add an application wich authorize Power BI Service?
(I've already done that)
#3
Do I need to create a Workspace for Power BI Embedded here https://portal.azure.com/#create/Microsoft.PowerBI ?
To me it seems there's to many ways to implement Power BI Embedded in a web app. I am lost.
Thank you