Azure AD Token based Authentication for WebAPI - azure

Question

We have developed Web API in .net Core 2.1 without authentication.
But now we are trying to add the Azure AD token based authentication.
we have registered app in azure AD and we did necessary changes in startup.cs file. and added authorize tag
When we test the API in postman we generated token we are getting Microsoft login page in Html format as result.
when we crosscheck the API in browser, its asking domain user name and password by providing the user name password we are getting the result.
Its seems some configuration or setting missing in Azure AD setup or code.
Can anyone help on this. other wise anyone share the steps for token based authentication implementation for API.

Answer 1

If you already have the api , you should firstly register an app in Azure Portal .
In your api application , you can follow the below steps :
Install the package Microsoft.AspNetCore.Authentication.AzureAD.UI
Register the Azure AD Bearer authentication service in ConfigureServices function :
services.AddAuthentication(AzureADDefaults.BearerAuthenticationScheme)
.AddAzureADBearer(options => Configuration.Bind("AzureAd", options));
In appsettings.json , set the correct api configuration from Azure Portal :
"AzureAd": {
"Instance": "https://login.microsoftonline.com/",
"Domain": "YourDomain.onmicrosoft.com",
"TenantId": "cb1c3f2e-a2dd-4fde-bf8f-f75ab18b21ac",
"ClientId": "83bf146d-4948-4596-a4b3-b7b2e68ac3e0"
},
Tenant ID ,domain name and API's ClientId could be find in Azure Portal .Then you can add Authorize attribute on protected controllers/actions . If you have multiple authentication schema , you can authorize with a specific scheme .
You client app will uses the OpenID Connect middleware and the ADAL/MSAL to obtain a JWT bearer token for the signed-in user using the OAuth 2.0 protocol. The bearer token is passed to the web API, which validates the token and authorizes the user using the JWT bearer authentication middleware.