That extension method
/// <summary>
/// Extension method for authenticate.
/// </summary>
/// <param name="context">The <see cref="HttpContext"/> context.</param>
/// <param name="scheme">The name of the authentication scheme.</param>
/// <returns>The <see cref="AuthenticateResult"/>.</returns>
public static Task<AuthenticateResult> AuthenticateAsync(this HttpContext context, string scheme) =>
context.RequestServices.GetRequiredService<IAuthenticationService>().AuthenticateAsync(context, scheme);
goes through the IServiceProvider RequestServices
property.
/// <summary>
/// Gets or sets the <see cref="IServiceProvider"/> that provides access to the request's service container.
/// </summary>
public abstract IServiceProvider RequestServices { get; set; }
Mock the service provider to return a mocked IAuthenticationService
and you should be able to fake your way through the test.
authServiceMock.AuthenticateAsync(Arg.Any<HttpContext>(), Arg.Any<string>())
.Returns(Task.FromResult(AuthenticateResult.Success()));
providerMock.GetService(typeof(IAuthenticationService))
.Returns(authServiceMock);
httpContextMock.RequestServices.Returns(providerMock);
//...