If the SUT uses a Bearer Authentication Scheme with IdentityServer, "Bearer" scheme already exists

When looking at this document, it appears to work fine when using a basic authentication scheme, but when the Startup of the SUT contains the following, and an attempt is made to use a custom Bearer Auth scheme as per the doc, the error "Bearer" scheme already exists:

`services
.AddAuthentication(IdentityServerAuthenticationDefaults.AuthenticationScheme)
.AddIdentityServerAuthentication(options =>
{
options.Authority = "https://myidentityserver.com";
});`

Is there a simple way to override the IdentityServer configuration from the SUT?

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* ID: 77889d43-fedb-f8b4-8fea-379ec946555c
* Version Independent ID: f499b131-8b14-7e10-1728-543fdd5a5656
* Content: [Integration tests in ASP.NET Core](https://docs.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-3.0)
* Content Source: [aspnetcore/test/integration-tests.md](https://github.com/dotnet/AspNetCore.Docs/blob/master/aspnetcore/test/integration-tests.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-test**
* GitHub Login: @Rick-Anderson
* Microsoft Alias: **riande**