diff --git a/aspnetcore/security/authentication/index.md b/aspnetcore/security/authentication/index.md
index 07f1eb90c647..b40c947fa65d 100644
--- a/aspnetcore/security/authentication/index.md
+++ b/aspnetcore/security/authentication/index.md
@@ -48,13 +48,22 @@ The Authentication middleware is added in `Program.cs` by calling <xref:Microsof
 Authentication is responsible for providing the <xref:System.Security.Claims.ClaimsPrincipal> for authorization to make permission decisions against. There are multiple authentication scheme approaches to select which authentication handler is responsible for generating the correct set of claims:
 
 * [Authentication scheme](#authentication-scheme)
-* The default authentication scheme, discussed in the next section.
+* The default authentication scheme, discussed in the next two sections.
 * Directly set <xref:Microsoft.AspNetCore.Http.HttpContext.User?displayProperty=nameWithType>.
 
-There's no automatic probing of schemes. If the default scheme isn't specified, the scheme must be specified in the authorize attribute, otherwise, the following error is thrown:
+When there is only a single authentication scheme registered, it becomes the default scheme. If multiple schemes are registered and the default scheme isn't specified, a scheme must be specified in the authorize attribute, otherwise, the following error is thrown:
 
 > InvalidOperationException: No authenticationScheme was specified, and there was no DefaultAuthenticateScheme found. The default schemes can be set using either AddAuthentication(string defaultScheme) or AddAuthentication(Action\<AuthenticationOptions> configureOptions).
 
+### `DefaultScheme`
+
+When there is only a single authentication scheme registered, the single authentication scheme:
+
+* Is automatically used as the `DefaultScheme`.
+* Eliminates the need to specify the `DefaultScheme` in `AddAuthentication` or <xref:Microsoft.Extensions.DependencyInjection.AuthenticationCoreServiceCollectionExtensions.AddAuthenticationCore(Microsoft.Extensions.DependencyInjection.IServiceCollection,System.Action{Microsoft.AspNetCore.Authentication.AuthenticationOptions})>.
+
+To disable automatically using the single authentication scheme as the `DefaultScheme`, call `AppContext.SetSwitch("Microsoft.AspNetCore.Authentication.SuppressAutoDefaultScheme")`.
+
 ### Authentication scheme
 
 The [authentication scheme](xref:security/authorization/limitingidentitybyscheme) can select which authentication handler is responsible for generating the correct set of claims. For more information, see [Authorize with a specific scheme](xref:security/authorization/limitingidentitybyscheme).