Stormpath's .NET Developer Evangelist, Nate Barbettini, walks us through token authentication in ASP.NET Core. You will learn how sessions work, how token authentication works, and some of the intricacies of token authentication with ASP.NET Core.

1. TOKEN AUTHENTICATION
in ASP.NET Core
Nate Barbettini
@nbarbettini

2. Welcome!
• Agenda
• Stormpath 101 (5 mins)
• Get Started with iOS (40 mins)
• Q&A (10 mins)
• Remy Champion
Marketing
• Nate Barbettini
.NET Developer Evangelist

3. Speed to Market & Cost Reduction
• Complete Identity solution out-of-the-box
• Security best practices and updates by default
• Clean & elegant API/SDKs
• Little to code, no maintenance

4. Stormpath User Management

5. Overview
● How Sessions Work (And Why They Suck)
● How Token Authentication Works
● Tokens + ASP.NET Core

6. How Sessions Work
Browser
ASP.NET
(1) POST /login
(2) 200 OK
Set-Cookie: session=dh7jWkx8fj;
(3) GET /profile
(4) 200 OK
Cookie: session=dh7jWkx8fj;
Log In:
nate@example.com
MySecretPassword123!
Open Profile Page
Profit!
Session
Store

7. Drawbacks of Sessions
● Scaling is hard
● Doesn’t work with mobile

8. How Token Authentication Works
Browser
ASP.NET
(1) POST /login
(2) 200 OK
eyJ0eXAiOiJKV...
Stored token: eyJ0eXAiOiJKV...
(3) GET /profile
(4) 200 OK
Authorization: Bearer eyJ0eXAiOiJKV...
Log In:
nate@example.com
MySecretPassword123!
Open Profile View
Profit!

9. Advantages of Tokens
Stateless!
Works on both web and mobile
Flexible

10. ● A JWT is a JSON object that’s been stringified and base64-encoded:
Anatomy of JSON Web Tokens
eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJPbmxpb
mUgSldUIEJ1aWxkZXIiLCJpYXQiOjE0NjU1ODAwNzEsImV4cCI6MTQ
5NzExNjA3NywiYXVkIjoid3d3LmV4YW1wbGUuY29tIiwic3ViIjoib
mF0ZUBleGFtcGxlLmNvbSIsImlzQXdlc29tZSI6InRydWUiLCJwcm9
2aWRlcyI6WyJzdGF0ZWxlc3MiLCJhdXRoZW50aWNhdGlvbiJdfQ.VX
rLbyQeJfDmwTAg-JnRsyD23RYMQJshTx79z2STu0U
Red = Header
Blue = Payload (“claims”)
Green = Cryptographic signature (JWS)

11. Anatomy of JSON Web Tokens
{
typ: "JWT",
alg: "HS256"
}
{
iss: "Online JWT Builder",
iat: 1465580071,
exp: 1497116077,
aud: "www.example.com",
sub: "nate@example.com",
isAwesome: "true",
provides: [
"stateless",
"authentication"
]
}
Header
Body

12. ● Cryptographically signed by the server
● Signature guarantees it hasn’t been forged or altered
Token Security

13. ● Token expiration (exp claim) and not-before (nbf claim)
● Optional token revocation using a nonce (jti claim)
● Use HTTPS (TLS) everywhere!
● Store tokens securely
Token Security

14. Where to Store Tokens?
● On mobile: local device storage, sent via HTTP headers
● On the web: cookies, or HTML5 web storage (via HTTP headers)

15. Where to Store Tokens?
● HTML5 web storage: vulnerable to XSS (cross-site scripting)
● Cookies: not vulnerable to XSS
○ Set the HttpOnly and Secure flags
○ Still need to protect against CSRF
● More info: Stormpath blog
https://stormpath.com/blog/where-to-store-your-jwts-cookies-vs-html5-web-storage

16. Generating Tokens in ASP.NET Core
● This functionality was included in ASP.NET, but was removed from
ASP.NET Core.
● The community has stepped up to build this functionality:
○ Stormpath ASP.NET Core plugin
○ Thinktecture IdentityServer4
○ AspNet.Security.OpenIdConnect.Server
○ OpenIddict

17. ● Basic JWT creation: JwtSecurityTokenHandler
Generating Tokens in ASP.NET Core
using System.IdentityModel.Tokens.Jwt;
var claims = new Claim[]
{
new Claim(JwtRegisteredClaimNames.Sub, username),
new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
};
// Create the JWT and write it to a string
var jwt = new JwtSecurityToken(
issuer: _options.Issuer,
audience: _options.Audience,
claims: claims,
notBefore: now,
expires: now.Add(TimeSpan.FromMinutes(5)),
signingCredentials: _options.SigningCredentials);
var encodedJwt = new JwtSecurityTokenHandler().WriteToken(jwt);

18. ● Nate’s simple example on Github:
https://github.com/nbarbettini/SimpleTokenProvider
Generating Tokens in ASP.NET Core

19. Validating Tokens in ASP.NET Core
● Validating incoming Bearer (HTTP header) tokens is easy!
var mySecretKey = new SymmetricSecurityKey(
Encoding.ASCII.GetBytes("mysupersecret_secretKey!123"));
app.UseJwtBearerAuthentication(new JwtBearerOptions()
{
AutomaticAuthenticate = true,
TokenValidationParameters = new TokenValidationParameters()
{
IssuerSigningKey = mySecretKey,
ValidateLifetime = true,
ValidIssuer = "MyApplication",
ValidAudience = "https://app.example.com",
}
});

20. Validating Tokens in ASP.NET Core
● JWTs in cookies?
See SimpleTokenProvider on Github.

21. ● Hosted user identity and authentication/authorization API
● Token generation and authentication
● Single Sign-On across multiple applications
● Multi-tenant support for SaaS applications
● Free (forever) developer tier
About Stormpath

22. Token authentication in ASP.NET Core tutorial
https://stormpath.com/blog/token-authentication-asp-net-core
Stormpath + ASP.NET Core quickstart
https://docs.stormpath.com/dotnet/aspnetcore/latest/quickstart.html
Web storage vs. cookies
https://stormpath.com/blog/where-to-store-your-jwts-cookies-vs-html5-web-storage
Nate’s SimpleTokenProvider sample
https://github.com/nbarbettini/SimpleTokenProvider
Q&A

23. Thank you!
Nate Barbettini
@nbarbettini
recaffeinate.co
.ws