In ASP.NET Core 3.0 API, how do I implement JWT Bearer Tokens - asp.net-core-mvc

Question

I am starting on a new web API and I want to use ASP.NET Core 3.0. I also want to authorize callers to my API using JWTs and Azure AD as the Identity Provider.
I have set up many ASP.NET Core 2.x web APIs using JWTs and Azure AD that have worked just fine, however, when I try the same methods using ASP.NET Core 3.0 I get a 401 every time I try to access the API.
In my ASP.NET Core 2.2 web API, in Startup.cs I have the following in the ConfigureServices method;
// Add Azure AD OAUTH2.0 Authentication Services
services.AddAuthentication(sharedOptions =>
{
sharedOptions.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
})
.AddAzureAdBearer(options => Configuration.Bind("AzureAd", options));
And I have an AzureAd section in my appsettings.json file that have values for...
"AzureAd": {
"Instance": "https://login.microsoftonline.com/",
"Domain": "mydomain.com",
"TenantId": "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX", //<-- Directory ID for mydomain.com
"ClientId": "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" //<-- Application ID of web API as a registered application in mydomain.com domain
},
Then in Startup.cs --> Configure method, I have ...
app.UseAuthentication();
app.UseMvc();
And finally, I decorate my API controller with...
[Authorize]
And this all works just fine for ASP.NET Core 2.2.
However, after creating a new project for an ASP.NET Core 3.0 Web API, and trying to implement the same techniques, I always get an HTTP 401 status code.
I realize the ASP.NET Core 3.0 was just released and I have to assume that the issue is related to changes in the way Core 3.0 operates, but I am having difficulty finding a solution.
Update 10/2/19
I test my APIs using Postman. In Postman, I make a POST to Azure AD with the correct values needed to obtain the access token from Azure AD. I copy that valid token to the Authorization header in a GET request to my API.
If I set my API to ASP.NET Core 2.2 and run it, then test the API using Postman as described above, my API authorizes the request and returns the correct data in the GET request's response.
If I change the API to ASP.NET Core 3.0 and try it again, I always get an HTTP 401.
The issue has to be a difference between how ASP.NET Core 3.0 handles JWT authorization and how ASP.NET Core 2.2 does it.