Token-Based Authentication in ASP.NET Core

Scenario

Suppose you have an ASP.NET Core application where you want to implement token-based authentication for an AngularJS application. The AngularJS application will make a request to a specific URL passing a username and password. The Web API will authorize the user and return an access token, which the AngularJS app will use in subsequent requests.

How to Configure Token-Based Authentication in ASP.NET Core

To configure your ASP.NET Core Web API application for token-based authentication:

1. Define Constants

Create constants for the token audience and issuer:

const string TokenAudience = "Myself";
const string TokenIssuer = "MyProject";

2. Configure Services

In your Startup.cs file, add the following to the ConfigureServices method:

var keySecret = authenticationConfiguration["JwtSigningKey"];
var symmetricKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(keySecret));

services.AddTransient(_ => new JwtSignInHandler(symmetricKey));

services.AddAuthentication(options =>
{
    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
})
    .AddJwtBearer(options =>
    {
        options.TokenValidationParameters.ValidateIssuerSigningKey = true;
        options.TokenValidationParameters.IssuerSigningKey = symmetricKey;
        options.TokenValidationParameters.ValidAudience = JwtSignInHandler.TokenAudience;
        options.TokenValidationParameters.ValidIssuer = JwtSignInHandler.TokenIssuer;
    });

3. Set Up Authentication

Add the following line in your Startup.cs file, before any middleware that requires user information:

app.UseAuthentication();

4. Build the Token

Create a class to handle JWT token generation:

class JwtSignInHandler
{
    public const string TokenAudience = "Myself";
    public const string TokenIssuer = "MyProject";
    private readonly SymmetricSecurityKey key;

    public JwtSignInHandler(SymmetricSecurityKey symmetricKey)
    {
        this.key = symmetricKey;
    }

    public string BuildJwt(ClaimsPrincipal principal)
    {
        var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

        var token = new JwtSecurityToken(
            issuer: TokenIssuer,
            audience: TokenAudience,
            claims: principal.Claims,
            expires: DateTime.Now.AddMinutes(20),
            signingCredentials: creds
        );

        return new JwtSecurityTokenHandler().WriteToken(token);
    }
}

5. Return the Token

In the controller action where you want to return the token, call the BuildJwt method:

[HttpPost]
public string AnonymousSignIn([FromServices] JwtSignInHandler tokenFactory)
{
    var principal = new System.Security.Claims.ClaimsPrincipal(new[]
    {
        new System.Security.Claims.ClaimsIdentity(new[]
        {
            new System.Security.Claims.Claim(System.Security.Claims.ClaimTypes.Name, "Demo User")
        })
    });
    return tokenFactory.BuildJwt(principal);
}

With these steps, your ASP.NET Core Web API application will be configured to use token-based authentication, enabling your AngularJS application to securely access protected resources.

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