Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SpaServices.ReactDevelopmentServer;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using System.Text;
using InternFinder.Services;
using InternFinder.Helpers;
using Microsoft.AspNetCore.Http;
using MongoDB.Driver;

namespace server
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews().AddJsonOptions(options =>
            {
                // ignores null values during the default serialization
                options.JsonSerializerOptions.IgnoreNullValues = true;
            });

            // dependency injections
            // injecting the mongodb client
            services.AddSingleton<IMongoClient, MongoClient>(s =>
            {
                var connectionUri = s.GetRequiredService<IConfiguration>()["ConnectionStrings:HyphenDb"];
                return new MongoClient(connectionUri);
            });
            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>(); // used for injecting the HttpContext into the controllers

            // configure Dependency Injection for the following application services
            services.AddScoped<IUserService, UserService>();
            services.AddScoped<IEmailService, EmailService>();
            services.AddScoped<ICompanyService, CompanyService>();
            services.AddScoped<IGeneralService, GeneralService>();

            // In production, the React files will be served from this directory
            services.AddSpaStaticFiles(configuration =>
            {
                configuration.RootPath = "./ClientApp/build";
            });

            // Adding Authentication  
            services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            })

            // Adding Jwt Bearer  
            .AddJwtBearer(options =>
              {
                  options.SaveToken = true;
                  options.RequireHttpsMetadata = false;
                  options.TokenValidationParameters = new TokenValidationParameters()
                  {
                      ValidateIssuer = false,
                      ValidateIssuerSigningKey = true,
                      ValidateAudience = false,
                      IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["JWT:Secret"])),
                      ClockSkew = TimeSpan.Zero,
                      ValidateLifetime = true
                  };
              });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseSpaStaticFiles();
            app.UseRouting();
            app.UseAuthentication();
            app.UseAuthorization();
            // custom jwt auth middleware
            app.UseMiddleware<JwtMiddleware>();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "api/{controller}/{action=Index}/{id?}");
            });

            app.UseSpa(spa =>
            {
                spa.Options.SourcePath = "./ClientApp";

                if (env.IsDevelopment())
                {
                    spa.UseReactDevelopmentServer(npmScript: "start");
                }
            });
        }
    }
}