Jmprieur/sync from web api tutorial (#186)

* Synching the generation of the wwwAuthenticate header
in TokenAcquisition.cs from the code which is currently
in the ASP.NET Core Web API tutorial

* Fix configuration binding in Web API

Author: jmprieur

Diff for: Microsoft.Identity.Web/WebApiServiceCollectionExtensions.cs

@@ -38,20 +38,18 @@ public static IServiceCollection AddProtectedWebApi(
             this IServiceCollection services,
             IConfiguration configuration,
             X509Certificate2 tokenDecryptionCertificate = null,
-            string configSectionName = "AzureAD",
+            string configSectionName = "AzureAd",
             bool subscribeToJwtBearerMiddlewareDiagnosticsEvents = false)
         {
             services.AddAuthentication(AzureADDefaults.JwtBearerAuthenticationScheme)
                     .AddAzureADBearer(options => configuration.Bind(configSectionName, options));
+            services.Configure<AzureADOptions>(options => configuration.Bind(configSectionName, options));
 
             services.AddHttpContextAccessor();
 
             // Change the authentication configuration to accommodate the Microsoft identity platform endpoint (v2.0).
             services.Configure<JwtBearerOptions>(AzureADDefaults.JwtBearerAuthenticationScheme, options =>
             {
-                // Reinitialize the options as this has changed to JwtBearerOptions to pick configuration values for attributes unique to JwtBearerOptions
-                configuration.Bind(configSectionName, options);
-
                 // This is an Microsoft identity platform Web API
                 options.Authority += "/v2.0";