Issue while generating Embed token with ClientID and login credentials using EmbedApiSample

My requirement is to use the PowerBI embedded to show the .pbix reports in a angular web application.

I'm getting the following error when I try to run this app (https://github.com/guyinacube/Embed-API-Sample) to create Embed token (as specified in the video https://www.youtube.com/watch?v=GPHHdDRSlis&list=PLv2BtOtLblH2Rm9trJPuxmN8Kr8WFv7O0&index=7). The console application is crashing when it is trying to authenticate the credentials.

{"AADSTS70002: The request body must contain the following parameter: 'client_secret or client_assertion'.\r\nTrace ID: 4de61335-1397-4912-ba59-62986ddc6200\r\nCorrelation ID: c7a41f92-4279-45c5-8ecf-f67dbb85d225\r\nTimestamp: 2018-04-23 15:20:09Z"}

It is breaking with the above exception when it executes the line

 authenticationResult = await authenticationContext.AcquireTokenAsync(resourceUrl, Secrets.ClientID, credential);

I Registered my application with the Power BI App Registration Tool in the link https://dev.powerbi.com/apps

I provided the following details during registration:

App Type:
    Server-side Web app
Redirect URL:
    http://localhost:4200/main/homepage
Home Page URL:
    http://localhost:4200

After registering the application with above details, I got both Client ID & Client Secret. In the console I could provide the ClientID, my login credentials, but not able to provide Client Secret. When I execute the application and during the authentication the application is crashing.

Why I am getting this error? How to generate the Embed token?