Using Oauth to protect WebAPI with Azure active directory - azure

Question

I have browsed all the tutorials regarding using Oauth to protect WebAPI in Azure active directory online. But unfortunately, none of them can work.
I am using VS 2017 and my project is .net core.
So far what I have tried is:
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
ervices.AddAuthentication(); // -----------> newly added
}
In "Configure", I added:
app.UseJwtBearerAuthentication(new JwtBearerOptions
{
AutomaticAuthenticate = true,
AutomaticChallenge = true,
Authority = String.Format(Configuration["AzureAd:AadInstance"], Configuration["AzureAD:Tenant"]),
Audience = Configuration["AzureAd:Audience"],
});
Here is my config:
"AzureAd": {
"AadInstance": "https://login.microsoftonline.com/{0}",
"Tenant": "tenantname.onmicrosoft.com",
"Audience": "https://tenantname.onmicrosoft.com/webapiservice"
}
I have registered this "webapiservice" (link is: http://webapiservice.azurewebsites.net) on my AAD.
Also, to access this web api service, I created a webapi client "webapiclient" which is also a web api and also registered it on my AAD and requested permission to access "webapiservice". The webapi client link is: http://webapiclient.azurewebsites.net
HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://webapiservice.azurewebsites.net/");
//is this uri correct? should it be the link of webapi service or the one of webapi client?
HttpResponseMessage response = client.GetAsync("api/values").Result;
if (response.IsSuccessStatusCode)
{
var result = response.Content.ReadAsAsync<IEnumerable<string>>().Result;
return result;
}
else
{
return new string[] { "Something wrong" };
}
So theoretically, I should receive the correct results from webapiservice. but I always received "Something wrong".
Am I missing anything here?

Answer 1

You need an access token from Azure AD.
There are plenty of good example apps on GitHub, here is one for a Daemon App: https://github.com/Azure-Samples/active-directory-dotnet-daemon/blob/master/TodoListDaemon/Program.cs#L96
AuthenticationResult authResult = await authContext.AcquireTokenAsync(todoListResourceId, clientCredential);
This app fetches an access token with its client id and client secret for an API. You can follow a similar approach in your case. You can just replace todoListResourceId with "https://graph.windows.net/" for Azure AD Graph API, or "https://graph.microsoft.com/" for Microsoft Graph API, for example. That is the identifier for the API that you want a token for.
This is the way it works in AAD. You want access to an API, you ask for that access from AAD. In a successful response you will get back an access token, that you must attach to the HTTP call as a header:
Authorization: Bearer accesstokengoeshere......
Now if you are building a web application, you may instead want to do it a bit differently, as you are now accessing the API as the client app, not the user. If you want to make a delegated call, then you will need to use e.g. the Authorization Code flow, where you show the user a browser, redirect them to the right address, and they get sent back to your app for login.

Answer 2

To call web api protected by azure ad , you should pass this obtained access token in the authorization header using a bearer scheme :
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", authResult.AccessToken);