Pupli

Add Nuget Packages

Microsoft.AspNetCore.Authentication.JwtBearer
Microsoft.IdentityModel.Tokens
System.IdentityModel.Tokens.Jwt

Add setting in appsetting.json

"Jwt": {
    "Key": "ACDt1vR3lXToPQ1g3MyN", //Generate random String from https://www.random.org/strings
    "Issuer": "http://localhost:28747/", //Project Property-> Debug-> IIS-->App URL (you can local host url as well)
    "Audience": "http://localhost:28747/"
  },

Register JWT token for Authentication in Program.cs file

using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using System.Text;
var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
//JWT Authentication
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme).AddJwtBearer(options => {
    options.TokenValidationParameters = new TokenValidationParameters {
        ValidateIssuer = true,
            ValidateAudience = true,
            ValidateLifetime = true,
            ValidateIssuerSigningKey = true,
            ValidIssuer = builder.Configuration["Jwt:Issuer"],
            ValidAudience = builder.Configuration["Jwt:Audience"],
            IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Key"]))
    };
});
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment()) {
    app.UseSwagger();
    app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();
app.Run();

Create Models (UserLogin, UserModel and UserConstant)

namespace JWTLoginAuthenticationAuthorization.Models
{
    public class UserModel
    {
        public string Username { get; set; }
        public string Password { get; set; }
        public string Role { get; set; }
    }
}

namespace JWTLoginAuthenticationAuthorization.Models
{
    public class UserLogin
    {
        public string Username { get; set; }
        public string Password { get; set; }
    }
}

namespace JWTLoginAuthenticationAuthorization.Models
{
    // We are not taking data from data base so we get data from constant
    public class UserConstants
    {
        public static List<UserModel> Users = new()
            {
                    new UserModel(){ Username="naeem",Password="naeem_admin",Role="Admin"}
            };
    }
}

Create LoginAPI Controller (Authenticate user and generate token)

using JWTLoginAuthenticationAuthorization.Models;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.IdentityModel.Tokens;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;

namespace JWTLoginAuthenticationAuthorization.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class LoginController : ControllerBase
    {
        private readonly IConfiguration _config;
        public LoginController(IConfiguration config)
        {
            _config = config;
        }

        [AllowAnonymous]
        [HttpPost]
        public ActionResult Login([FromBody] UserLogin userLogin)
        {
            var user = Authenticate(userLogin);
            if (user != null)
            {
                var token = GenerateToken(user);
                return Ok(token);
            }

            return NotFound("user not found");
        }

        // To generate token
        private string GenerateToken(UserModel user)
        {
            var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_config["Jwt:Key"]));
            var credentials = new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256);
            var claims = new[]
            {
                new Claim(ClaimTypes.NameIdentifier,user.Username),
                new Claim(ClaimTypes.Role,user.Role)
            };
            var token = new JwtSecurityToken(_config["Jwt:Issuer"],
                _config["Jwt:Audience"],
                claims,
                expires: DateTime.Now.AddMinutes(15),
                signingCredentials: credentials);


            return new JwtSecurityTokenHandler().WriteToken(token);

        }

        //To authenticate user
        private UserModel Authenticate(UserLogin userLogin)
        {
            var currentUser = UserConstants.Users.FirstOrDefault(x => x.Username.ToLower() ==
                userLogin.Username.ToLower() && x.Password == userLogin.Password);
            if (currentUser != null)
            {
                return currentUser;
            }
            return null;
        }
    }
}

Create User API Controller to authorize user role

namespace JWTLoginAuthenticationAuthorization.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class UserController : ControllerBase
    {
        //For admin Only
        [HttpGet]
        [Route("Admins")]
        [Authorize(Roles = "Admin")]
        public IActionResult AdminEndPoint()
        {
            var currentUser = GetCurrentUser();
            return Ok($"Hi you are an {currentUser.Role}");
        }
        private UserModel GetCurrentUser()
        {
            var identity = HttpContext.User.Identity as ClaimsIdentity;
            if (identity != null)
            {
                var userClaims = identity.Claims;
                return new UserModel
                {
                    Username = userClaims.FirstOrDefault(x => x.Type == ClaimTypes.NameIdentifier)?.Value,
                    Role = userClaims.FirstOrDefault(x => x.Type == ClaimTypes.Role)?.Value
                };
            }
            return null;
        }
    }
}

References
https://www.c-sharpcorner.com/article/jwt-token-creation-authentication-and-authorization-in-asp-net-core-6-0-with-po/
https://www.youtube.com/watch?v=UwruwHl3BlU
https://www.youtube.com/watch?v=6sMPvucWNRE