I have added ASP.NET Core identity and Identity Server4 in one project with one database, and I want to use my Identity Server in all other project.

IdentityServer4 Startup Class

public class Startup
{
    public IConfigurationRoot Config { get; set; }

    public Startup(IConfiguration configuration)
    {
        Config = new ConfigurationBuilder()
                     .SetBasePath(Directory.GetCurrentDirectory())
                     .AddJsonFile("appsettings.json", false)
                     .Build();

        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        IdentityModelEventSource.ShowPII = true;

        //=== Identity Config ===
        string ConnectionString = Config.GetSection("AppSettings:DefaultConnection").Value;
        var migrationAssembly = typeof(Startup).GetTypeInfo().Assembly.GetName().Name;

        //-----------------------------------------------------------------
        services.AddDbContext<MyIdentityDbContext>(options =>
             options.UseSqlServer(ConnectionString, sql => sql.MigrationsAssembly(migrationAssembly)));

        //-----------------------------------------------------------------
        services.AddIdentity<MyIdentityUser, IdentityRole>(op =>
        {
            op.Password.RequireDigit = false;
            op.Password.RequiredLength = 6;
            op.Password.RequireUppercase = false;
            op.Password.RequireLowercase = false;
            op.Password.RequireNonAlphanumeric = false;
        })
        .AddEntityFrameworkStores<MyIdentityDbContext>()
        .AddDefaultTokenProviders();

        //=== IdentityServer4 config ===
        services.AddIdentityServer(options =>
        {
            options.Events.RaiseErrorEvents = true;
            options.Events.RaiseInformationEvents = true;
            options.Events.RaiseFailureEvents = true;
            options.Events.RaiseSuccessEvents = true;
        })
            .AddDeveloperSigningCredential()
            .AddConfigurationStore(options =>
            {
                options.ConfigureDbContext = b => b.UseSqlServer(ConnectionString, sql => sql.MigrationsAssembly(migrationAssembly));
            })
            .AddOperationalStore(options =>
            {
                options.ConfigureDbContext = b => b.UseSqlServer(ConnectionString, sql => sql.MigrationsAssembly(migrationAssembly));
            })
            .AddAspNetIdentity<MyIdentityUser>();

        services.AddMvc(options => options.EnableEndpointRouting = false);
        services.AddAuthorization();
        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        app.UseAuthentication();
        app.UseRouting();

        app.UseAuthorization();
        app.UseIdentityServer();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

My config class that I have seed my identity database with that:

public class Config
{
    public static IEnumerable<IdentityResource> GetIdentityResources()
    {
        return new List<IdentityResource>
        {
            new IdentityResources.OpenId(),
            new IdentityResources.Email(),
            new IdentityResources.Profile(),
        };
    }

    public static IEnumerable<ApiResource> GetApis()
    {
        return new List<ApiResource>
        {
            new ApiResource("MyAPI", "My asp.net core web api"),
        };
    }

    public static IEnumerable<Client> GetClients()
    {
        return new List<Client>
        {
            new Client()
            {
                 ClientId = "MyAndroidApp",
                 ClientName = "My Application for Android",
                 AllowedGrantTypes = GrantTypes.ResourceOwnerPassword,
                 ClientSecrets =
                 {
                    new Secret("secret".Sha256())
                 },
                 AllowedScopes=
                 {
                     IdentityServerConstants.StandardScopes.OpenId,
                     IdentityServerConstants.StandardScopes.Profile,
                     IdentityServerConstants.StandardScopes.Email,
                     IdentityServerConstants.StandardScopes.Address,
                     "MyAPI"
                 },
            },
        };
    }
}

I have register a user with role Admin with below action method in User controller in my IdentityServer4&Identity project

[HttpPost]
public async Task<IActionResult> Post([FromBody]SignUpModel model)
{                               
    MydentityUser NewUser = new MydentityUser ()
            {
                UserName = model.UserName,
            };
    IdentityResult result = await UserManager.CreateAsync(NewUser, model.Password);

    if (result.Succeeded)
    {
        if (!RoleManager.RoleExistsAsync("Admin").Result)
        {
            IdentityResult r = RoleManager.CreateAsync(new IdentityRole("Admin")).Result;
            r = RoleManager.CreateAsync(new IdentityRole("Member")).Result;
            r = RoleManager.CreateAsync(new IdentityRole("Guest")).Result;
        }

        result = await UserManager.AddToRoleAsync(NewUser, "Admin");

        if (result.Succeeded)
        {
            List<Claim> UserClaims = new List<Claim>() {
                    new Claim("userName", NewUser.UserName),
                    new Claim(JwtClaimTypes.Role, "Admin"),
                };

            result = await UserManager.AddClaimsAsync(NewUser, UserClaims.ToArray());
            return Ok("Registered");
        }
    }            
}

Now I have another ASP.NET Web API project that I want to use this api in my android application.

My startup class

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication(IdentityServerAuthenticationDefaults.AuthenticationScheme)
            .AddJwtBearer(options =>
            {
                options.Authority = "https://identity.mywebsite.ir";
                options.RequireHttpsMetadata = false;
                options.Audience = "MyAPI";                    
            });
         //I used below but not work too
        //.AddIdentityServerAuthentication(options =>
        //{
        //    options.Authority = "https://identity.mywebsite.ir";
        //    options.RequireHttpsMetadata = false;
        //    options.ApiName = "MyAPI";
        //    options.NameClaimType = ClaimTypes.Name;
        //    options.RoleClaimType = ClaimTypes.Role;                    
        //});

        services.AddOptions();
        string cs = Configuration["AppSettings:DefaultConnection"];
        services.AddDbContext<MyApiContext>(options =>
        {
            options.UseSqlServer(cs,
                sqlServerOptions =>
                {
                    sqlServerOptions.MigrationsAssembly("MyApi.Database");
                });
        });

        services.AddControllers();

        services.AddCors(options =>
        {
            options.AddPolicy("default", policy =>
            {
                policy.WithOrigins("*")
                    .AllowAnyHeader()
                    .AllowAnyMethod();
            });
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        app.UseRouting();
        app.UseCors("default");
        app.UseAuthentication();
        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

My Problem is how can I find userId in my Webapi when I have used user authentication with ASP.NET Core Identity in another project,

I have below action method in my two project (my webapi and identityserver & identity project). I have get token from android application from /connect/token address and I send access token with my request.

public class TestController : ControllerBase
{
    public async Task<IActionResult> Index()
    {            
        string message = "";

        if (User.Identity.IsAuthenticated)
        {
            message += "You are Registered ";
        }
        else
        {
            message += "You are not Registered ";
        }

        if (string.IsNullOrWhiteSpace(User.Identity.Name))
        {
            message += "UserId is null";
        }
        else
        {
            message += "UserId is not null";
        }

        return Ok(message);
    }
}

I get this message:

You are not registered UserId is null

How can I access to my UserId in my WebAPI? Why User.Identity.Name is null? Why is User.Identity.Claims.Count 0?

Edit

I have entered the access token in jwt.io website, this is the output

{
  "nbf": 1587133648,
  "exp": 1587137248,
  "iss": "https://identity.mywebsite.ir",
  "aud": "MyAPI",
  "client_id": "MyAndroidApp",
  "sub": "7e904278-78cc-46a8-9943-51dfeb360d8e",// I want this in my api but i get null
  "auth_time": 1587133648,
  "idp": "local",
  "scope": [
    "openid",
    "MyAPI"
  ],
  "amr": [
    "pwd"
  ]
}

MyApi Startup Class

 public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = IdentityServerAuthenticationDefaults.AuthenticationScheme;
                options.DefaultChallengeScheme = "oidc";
            })

        .AddIdentityServerAuthentication(options =>
        {
            options.Authority = "https://identity.mywebsite.ir";
                options.RequireHttpsMetadata = false;
            options.ApiName = "MyAPI";
            });

            services.AddOptions();
            string cs = Configuration["AppSettings:DefaultConnection"];
            services.AddDbContext<MyCommonDbContext>(options =>
            {
                options.UseSqlServer(cs,
                    sqlServerOptions =>
                    {
                        sqlServerOptions.MigrationsAssembly("MyAppProjectName");
                    });
            });
            services.AddDbContext<MyAppContext>(options =>
            {
                options.UseSqlServer(cs,
                    sqlServerOptions =>
                    {
                        sqlServerOptions.MigrationsAssembly("MyAppProjectName");
                    });
            });

            services.AddControllers();

            services.AddCors(options =>
            {
                options.AddPolicy("default", policy =>
                {
                    policy.WithOrigins("http://*.mywebsite.ir")
                        .AllowAnyHeader()
                        .AllowAnyMethod();
                });
            });
        }
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseRouting();
            app.UseCors("default");
            app.UseAuthentication();
            app.UseAuthorization();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }