An example how to test a middleware or message handler, which uses `HttpContext.GetTokenAsync("access_token")`

Example.cs

//
// `GetTokenAsync` usage
//

protected override async Task<HttpResponseMessage> SendAsync(
    HttpRequestMessage request,
    CancellationToken cancellationToken)
{
    request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", _httpContextAccessor.HttpContext.GetTokenAsync("access_token").Result);

    return await base.SendAsync(request, cancellationToken);
}


//
// Mocking it in unit test
//

// Arrange 
var httpRequestMessage = new HttpRequestMessage(HttpMethod.Get, "http://test.com");

var authProps = new AuthenticationProperties();
authProps.StoreTokens(new List<AuthenticationToken>
{
    new AuthenticationToken{ Name = "access_token", Value = "test-jwt"}
});

var authenticationServiceMock = new Mock<IAuthenticationService>();
authenticationServiceMock.Setup(x => x.AuthenticateAsync(It.IsAny<HttpContext>(), It.IsAny<string>()))
    .ReturnsAsync(AuthenticateResult.Success(new AuthenticationTicket(new ClaimsPrincipal(), authProps, "Bearer")));

var serviceProviderMock = new Mock<IServiceProvider>();
serviceProviderMock
    .Setup(s => s.GetService(typeof(IAuthenticationService)))
    .Returns(authenticationServiceMock.Object);

var context = new DefaultHttpContext()
{
    RequestServices = serviceProviderMock.Object
};

var contextAccessor = new Mock<IHttpContextAccessor>();
contextAccessor.Setup(x => x.HttpContext).Returns(context);

var handler = new AuthorizationHttpMessageHandler(contextAccessor.Object)
{
    InnerHandler = new TestHandler((r, c) =>
    {
        // Assert 1
        Assert.Equal("Bearer", r.Headers.Authorization.Scheme);
        Assert.Equal("test-jwt", r.Headers.Authorization.Parameter);
        return TestHandler.Return200();
    })
};

var client = new HttpClient(handler);

// Act
var result = client.SendAsync(httpRequestMessage).Result;

// Assert 2
Assert.Equal(HttpStatusCode.OK, result.StatusCode);