Program.cs

using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using Microsoft.OpenApi.Models;
using MinimalAPIAuthentication.Models;
using System.IdentityModel.Tokens.Jwt;
using System.Text;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(option =>
{
    option.SwaggerDoc("v1", new OpenApiInfo { Title = "Demo API", Version = "v1" });
    option.AddSecurityDefinition("Bearer", new OpenApiSecurityScheme
    {
        In = ParameterLocation.Header,
        Description = "Please enter a valid token",
        Name = "Authorization",
        Type = SecuritySchemeType.Http,
        BearerFormat = "JWT",
        Scheme = "Bearer"
    });
    option.AddSecurityRequirement(new OpenApiSecurityRequirement
    {
        {
            new OpenApiSecurityScheme
            {
                Reference = new OpenApiReference
                {
                    Type=ReferenceType.SecurityScheme,
                    Id="Bearer"
                }
            },
            new string[]{}
        }
    });
});
builder.Services.AddAuthentication(options =>
{
    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
    options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
}).AddJwtBearer(o =>
{
    o.TokenValidationParameters = new TokenValidationParameters
    {
        ValidIssuer = builder.Configuration["Jwt:Issuer"],
        ValidAudience = builder.Configuration["Jwt:Audience"],
        IssuerSigningKey = new SymmetricSecurityKey
        (Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Key"])),
        ValidateIssuer = true,
        ValidateAudience = true,
        ValidateLifetime = false,
        ValidateIssuerSigningKey = true
    };
});
builder.Services.AddAuthorization();
var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateTime.Now.AddDays(index),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
})
.WithName("GetWeatherForecast").RequireAuthorization();
app.MapPost("/createToken",
[Microsoft.AspNetCore.Authorization.AllowAnonymous] (User user) =>
{
    if (user.UserName == builder.Configuration["UserSecrets:UserName"] && user.Password == builder.Configuration["UserSecrets:Password"])
    {
        var issuer = builder.Configuration["Jwt:Issuer"];
        var audience = builder.Configuration["Jwt:Audience"];
        var key = Encoding.ASCII.GetBytes
        (builder.Configuration["Jwt:Key"]);
        var tokenDescriptor = new SecurityTokenDescriptor
        {
            Subject = new System.Security.Claims.ClaimsIdentity(new[]
            {
                new System.Security.Claims.Claim("Id", Guid.NewGuid().ToString()),
                new System.Security.Claims.Claim(JwtRegisteredClaimNames.Sub, user.UserName),
                new System.Security.Claims.Claim(JwtRegisteredClaimNames.Email, user.UserName),
                new System.Security.Claims.Claim(JwtRegisteredClaimNames.Jti,
                Guid.NewGuid().ToString())
             }),
            Expires = DateTime.UtcNow.AddMinutes(5),
            Issuer = issuer,
            Audience = audience,
            SigningCredentials = new SigningCredentials
            (new SymmetricSecurityKey(key),
            SecurityAlgorithms.HmacSha512Signature)
        };
        var tokenHandler = new JwtSecurityTokenHandler();
        var token = tokenHandler.CreateToken(tokenDescriptor);
        var jwtToken = tokenHandler.WriteToken(token);
        var stringToken = tokenHandler.WriteToken(token);
        return Results.Ok(stringToken);
    }
    return Results.Unauthorized();
});
app.UseAuthentication();
app.UseAuthorization();
app.Run();

internal record WeatherForecast(DateTime Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}