[JWT in .Net Core] basic JWT implementation with roles

BL.cs

    public class AuthenticationBL : IAuthenticationBL
    {
        private readonly IAuthenticationRepository _authenticationRepository;
        private readonly IConfiguration _configuration;

        public AuthenticationBL(IAuthenticationRepository authenticationRepository, IConfiguration configuration)
        {
            _authenticationRepository = authenticationRepository;
            _configuration = configuration;
        }

        public async Task<LoginResult> HandleAdminLogin(AdminLoginRequest adminLoginRequest)
        {
            var admin = await _authenticationRepository.GetAdmin(
                adminLoginRequest.FirstName,
                adminLoginRequest.LastName
            );

            if (admin == null) return new LoginResult() { Reason = LoginResult.ResultReason.UserNotFound };

            if (adminLoginRequest.Password == null)
                return new LoginResult() { Reason = LoginResult.ResultReason.PasswordNotProvided };

            var correctPassword = ValidatePassword(adminLoginRequest.Password, admin.PasswordHash);
            if (!correctPassword) return new LoginResult() { Reason = LoginResult.ResultReason.PasswordIncorrect };

            var token = GenerateToken(admin);
            return new LoginResult() { Token = token, Reason = LoginResult.ResultReason.SuccessfulLogin };
        }

        private string GenerateToken(User admin)
        {
            var signingKeyBytes = Convert.FromBase64String(_configuration["JWT_SIGNING_KEY"]);
            var expiryDurationMinutes = int.Parse(_configuration["JWT_TOKEN_EXPIRY_DURATION_IN_MINUTES"]);

            var tokenDescriptor = new SecurityTokenDescriptor()
            {
                Expires = DateTime.UtcNow.AddMinutes(expiryDurationMinutes),
                Subject = new ClaimsIdentity(
                    new List<Claim>() { new Claim("role", "Administrator"), new Claim("userId", admin.Id) }
                ),
                IssuedAt = DateTime.UtcNow,
                NotBefore = DateTime.UtcNow,
                SigningCredentials = new SigningCredentials(
                    new SymmetricSecurityKey(signingKeyBytes),
                    SecurityAlgorithms.HmacSha256Signature
                )
            };

            var tokenHandler = new JwtSecurityTokenHandler();
            var tokenObject = tokenHandler.CreateJwtSecurityToken(tokenDescriptor);
            return tokenHandler.WriteToken(tokenObject);
        }
    }

Startup.cs

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

        private 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
                .AddMvc()
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

            services
                .AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(
                    options =>
                    {
                        var signingKeyBytes = Convert.FromBase64String(Configuration["JWT_SIGNING_KEY"]);
                        options.TokenValidationParameters = new TokenValidationParameters()
                        {
                            ValidateIssuerSigningKey = true,
                            IssuerSigningKey = new SymmetricSecurityKey(signingKeyBytes),
                            ValidateIssuer = false,
                            ValidateAudience = false,
                        };
                    }
                );

            services.AddScoped<IAuthenticationBL, AuthenticationBL>();
            services.AddScoped<IAuthenticationRepository, AuthenticationRepository>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                // 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.UseAuthentication();
            app.UseMvc();
        }
    }