@Edula Divya Siri Thank you for the question. I believe here you are trying to implement the Azure AD authentication to secure your application. I am sharing few relevant links which would help you implement the same:
https://learn.microsoft.com/en-us/azure/app-service/configure-authentication-provider-aad
https://stackoverflow.com/questions/32589063/unable-to-get-bearer-token-from-azure-ad-to-use-with-api-app [ navigate to the answer]
Please let me know if this answers or you need more details to understand how to implement authentication.