API Bearer token

// Startup.cs

using System.Reflection;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace App {
    public class Startup {

        private IConfiguration Configuration { get; }

        public Startup(IConfiguration configuration) {
            Configuration = configuration;
        }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services) {
            services.AddControllers();
            services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(JwtBearerDefaults.AuthenticationScheme, o => {
                    o.Authority = Configuration["Authority"];
                    o.RequireHttpsMetadata = false;
                    o.Audience = "api";
                    o.SaveToken = true;
                    o.TokenValidationParameters = new TokenValidationParameters { // verbatim from SO :)
                        IssuerSigningKeyResolver = (token, securityToken, keyIdentifier, tokenValidationParameters) =>
                        {
                            cache.TryGetValue("token");
                        }
                    };
                });
            services.AddAuthorization();
            services.AddHttpContextAccessor();

            // Microsoft.IdentityModel.Logging.IdentityModelEventSource.ShowPII = 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() || env.IsEnvironment("Local")) {
                app.UseDeveloperExceptionPage();
            }
            else {
                app.UseHsts();
            }


            app.UseAuthentication();
            app.UseHttpsRedirection();
            app.UseRouting();
            app.UseAuthorization();
            app.UseEndpoints(x => {
                x.MapControllers();
            });
        }
    }
}


/// HttpClientExtensions.cs

using System.Net.Http;
using System.Net.Http.Headers;

namespace App.Clients.Extensions {
    public static class HttpClientExtensions {
        internal static void InitHeaders(this HttpClient client, string token) {
            client.DefaultRequestHeaders.Clear();

            if(token != null) {
                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
            }

            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        }
    }
}


// SomeClient.cs

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Configuration;
using App.Clients.Extensions;

namespace App. Clients {
    public class SomeClient : HttpClient, ISomeClient{
        public SsoClient(IConfiguration config, IHttpContextAccessor http) {
            BaseAddress = new Uri(config["OpenId:Authority"]);
            var token = http.HttpContext.GetTokenAsync("access_token").Result;

            this.InitHeaders(token);
        }
    }
}