Token Authentication for Java Applications

Securing Web Applications
with Token Authentication
Les Hazlewood @lhazlewood
PMC Chair, Apache Shiro
Expert Group Member, JEE Application Security (JSR-375)
Founder & CTO, Stormpath

About Stormpath
• Authentication & User Management API
• Hosted data store w/ advanced crypto
• Centralize user login across your applications
• Multi-tenant support for your SaaS
• Active Directory, LDAP, social connections
• API authentication & token authentication
• Supported, Free tier for developers

Overview
• Security Concerns for Modern Web Apps
• Cookies: need to know
• Session ID Problems
• Token Authentication to the rescue!
• Java Example

Security Concerns for Modern Web Apps
• SPAs and Mobile apps are ‘Untrusted Clients’
• Prevent malicious code
• Secure user credentials
• Secure server endpoints (API)
• Expose Access Control rules to the Client
Learn more at Stormpath.com

Prevent Malicious Code
• Cross-Site Scripting (XSS) attacks are a real,
huge threat

Prevent Malicious Code
Cross-Site Scripting (XSS) attacks
https://www.owasp.org/index.php/XSS

XSS Attack
Demo
https://www.google.com/about/appsecurity/lear
ning/xss/#BasicExample

XSS Attack – What Can I Do?
Read EVERYTHING on this page:
https://www.owasp.org/index.php/XSS
And then do these things:
https://www.owasp.org/index.php/XSS_(Cross_Sit
e_Scripting)_Prevention_Cheat_Sheet

Escape Content!
Dynamic HTML: use well-known, trusted
libraries. Do NOT roll your own.
DOM attacks: escape user input

SPAs: frameworks like Angular probably do a
lot of work for you (e.g. preventing DOM
attacks by escaping user input).
You should still read up on it.

Secure User Credentials
• Traditionally, we have used Session IDs
• This is OK, as long as you do cookies ‘right’
• Authentication Tokens are better  (more on
this later)

Overview
• Security Concerns for Modern Web Apps
• Cookies: need to know
• Session ID Problems
• Token Authentication to the rescue!
• Java Example

Session ID Cookies

Secure Server (API) Endpoints
• Traditionally use Session ID Cookies
• Session ID  Session  User identity
• Use framework like Apache Shiro or Spring
Security to assert security rules

Expose Access Control Rules to the Client
• Traditional solution:
• Session ID  Session  User data in your DB
• Provide a /me or /profile endpoint
• Access Tokens are better!

Let’s talk about cookies...

Cookies are OK! If you do them correctly
Cookies can be easily compromised:
• Man-in-the-Middle (MITM) attacks
• Cross-Site Request Forgery (CSRF)

Man In The Middle (MITM) attacks
Someone ‘listening on the wire’ between the
browser and server can see and copy the
cookie.
Solutions
• Use HTTPS everywhere
• TLS everywhere on internal networks

Cross-Site Request Forgery (CSRF)
“... occurs when a malicious web site, email,
blog, instant message or program causes a
user’s web browser to perform an unwanted
action on a trusted site for which the user is
currently authenticated”
https://www.owasp.org/index.php/CrossSite_Re
quest_Forgery_(CSRF)_Prevention_Cheat_Sh
eet

Attacker enables a user to request your server.
Example:
<a
href=“https://yoursite.com/transferMo
ney?to=BadGuy&amount=10000”>See Cute
Cats!</a>
What happens?

• The attacker cannot see your cookie values,
BUT:
• The browser says, “The request is going to your
server, so I’ll happily send you your cookies.”
• Your server transfers the money because it
‘sees’ a valid, non-expired session id cookie for
an authenticated session.

Solutions
• Synchronizer Token
• Double-Submit Cookie
• Origin header check

Synchronizer Token – Trusted Page

Synchronizer Token – Foreign Page

Synchronizer Token - Considerations
• Requires cooperation from your rendering
layer
• Requires you to store tokens in a data store
or cache
• Difficult to do with static SPA content
• Only protects against forged POST requests,
not GETs!
Pro tip: never allow GETs to modify server state!

Double Submit Cookie
• Send two cookies: Session ID + Random
Value
• Send random value explicitly, browser Same-
Origin-Policy
• Best Way: send as a custom header

Double Submit Cookie

Double Submit Cookie Considerations
• Custom HTTP header, do what makes sense
for your app
• Still vulnerable to XSS - Random Value still
accessible to the JS environment.
• Protect against XSS!

Origin header check
• Browsers send Origin header
• Header value is the domain of the page
initiating the request
• Cannot be hacked via browser JS
(could still be modified by a malicious HTTP proxy
server)

Session ID Problems
• They’re opaque and have no meaning
themselves (they’re just ‘pointers’).
• Service-oriented architectures might need a
centralized ID de-referencing service

Session ID Problems
• Opaque IDs mean clients can’t inspect them
and find out what it is allowed to do or not - it
needs to make more requests for this
information.

Session ID Problems
• Sessions = Server State!
• You need to store that state somewhere
• Session ID  look up server state on *every
request*.
• Really not good for distributed/clustered apps
• Really not good for scale

Token Authentication
• What is Authentication?
• What is a Token?

JSON Web Tokens (JWT)
• A URL-safe, compact, self-contained string with
meaningful information that is usually digitally
signed or encrypted.
• The string is ‘opaque’ and can be used as a
‘token’.
• Many OAuth2 implementations use JWTs as
OAuth2 Access Tokens.

• You can store them in cookies! But all those
cookie rules still apply.
• You can entirely replace your session ID with
a JWT.

In the wild they look like just another ugly string:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJ
pc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQo
gImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnV
lfQ.dBjftJeZ4CVPmB92K27uhbUJU1p1r_wW1gFWFOEj
Xk

But they do have a three part structure. Each
part is a Base64-encoded string:
eyJ0eXAiOiJKV1QiLA0KICJhb
GciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJle
HAiOjEzMDA4MTkzODAsDQogIm
h0dHA6Ly9leGFtcGxlLmNvbS9
pc19yb290Ijp0cnVlfQ
.
dBjftJeZ4CVPmB92K27uhbUJU
1p1r_wW1gFWFOEjXk
Header
Body (‘Claims’)
Cryptographic Signature

Base64-decode the parts to find the juicy bits:
{
"typ":"JWT",
"alg":"HS256"
}
{
"iss”:”http://trustyapp.com/”,
"exp": 1300819380,
“sub”: ”users/8983462”,
“scope”: “self api/buy”
}
tß´—™à%O˜v+nî…SZu¯µ€U…8H×
Header
Body (‘Claims’)
Cryptographic Signature

The claims body is the best part! It can tell:
{
"exp": 1300819380,
“sub”: ”users/8983462”,
}
Who issued the token

{
"exp": 1300819380,
“sub”: ”users/8983462”,
}
When it expires

{
"exp": 1300819380,
“sub”: ”users/8983462”,
}
When it expires
Who it represents

{
"exp": 1300819380,
“sub”: ”users/8983462”,
}
When it expires
Who it represents
What they can do

Great! Why is this useful?
• Implicitly trusted because it is cryptographically
signed (verified not tampered).
• It is structured, enabling inter-op between
services
• It can inform your client about basic access
control rules (permissions)*
• And the big one: statelessness!
*servers must always enforce access control policies

So, what’s the catch?
• Implicit trust is a tradeoff – how long
should the token be good for? how will you
revoke it? (Another talk: refresh tokens)
• You still have to secure your cookies!
• You have to be mindful of what you store in
the JWT if they are not encrypted. No
sensitive info!

How do you do it on the JVM?
JJWT is awesome
https://github.com/jwtk/jjwt

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
byte[] key = getSignatureKey();
String jwt =
Jwts.builder().setIssuer(“http://trustyapp.com/”)
.setSubject(“users/1300819380”)
.setExpiration(expirationDate)
.put(“scope”, “self api/buy”)
.signWith(SignatureAlgorithm.HS256,key)
.compact();
Create a JWT:

Verify a JWT:
try {
Jws<Claims> jwt =
Jwts.parser().setSigningKey(key).parseClaimsJws(jwt);
//OK, we can trust this JWT
} catch (SignatureException e) {
//don't trust the JWT!
}

Demo!

Thanks!
@lhazlewood @goStormpath
• Token Authentication for Java, Spring and Spring Boot
• Free Supported Developer Tier
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• OSS Java SDKs + Tutorials
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Token Authentication for Java Applications

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