According the site “Register a SaaS application”
https://docs.microsoft.com/en-us/azure/marketplace/partner-center-portal/pc-saas-registrationAccording the part “Register an Azure AD-secured app”
Each SaaS offer must have own application for registration.
In the part “Get the token with an HTTP POST” in the site, where you acquire access token through the POST request to the site
https://login.microsoftonline.com/*{tenantId}*/oauth2/tokenensure that the body is written in exact this format:
grant_type=client_credentials&
client_id=CLIENT_ID_OF_YOUR_AZURE_REGISTRATION_APPLICATION&
client_secret=CLIENT_SECRET_OF_YOUR_AZURE_REGISTRATION_APPLICATION&
resource=20e940b3-4c77-4b0b-9a53-9e16a1b010a7
This registration application for the concrete SaaS offer must be encapsulated in Azure Login functionality.
Here is a very good example how to create such app in React:
https://docs.microsoft.com/en-us/azure/active-directory/develop/tutorial-v2-reactAround this site are also examples which use other technologies.