public void ConfigureServices(IServiceCollection services)
{

            /*...*/

            var key = Encoding.ASCII.GetBytes("9ST5hQe5dUNfAJOQZAtt19uiDhNtKKUt");
            var signingKey = new SymmetricSecurityKey(key);

            // Authenticate a request
            services.AddAuthentication(x =>
            {
                x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            })
            .AddJwtBearer(x =>
            {
                x.RequireHttpsMetadata = false;
                x.SaveToken = true;
                x.TokenValidationParameters = new TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = signingKey,
                    ValidateAudience = false,
                    ValidateIssuer = false
                };
            });
            // Custom policy to check if a certain claim has a certain value
            services.AddAuthorization(options =>
            {
                options.AddPolicy(
                    "IsAgentPolicy",
                    policy => policy.RequireClaim("aut", "ROLE_AGENT")
                );
            });

            /*...*/
}

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

            app.UseAuthentication();

            app.UseMvc();
        }

[Route("api/[controller]")]
    public class ValuesController : ControllerBase
    {
        // GET: api/<controller>
        [HttpGet]
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }

        // GET api/<controller>/5
        [HttpGet("{id}")]
        [Authorize("IsAgentPolicy")]
        public string Get(int id)
        {
            return "value";
        }
    }