securing web applications with token authentication

Securing Web Applications with Token AuthenticationMicah Silverman @afitnerdCo-Author, Mastering Enterprise JavaBeans 3.0Java Developer Evangelist, 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!

• OAuth2 & 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

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/learning/xss/#BasicExample

https://www.google.com/about/appsecurity/learning/xss/%23BasicExample

XSS Attack – What Can I Do?

Read EVERYTHING on this page:


And then do these things:

https://www.owasp.org/index.php/XSS_(Cross_Site_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





• Java Example

Session ID Cookies

Secure Server (API) Endpoints

• Traditionally use Session ID Cookies

• Session ID à Session à 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 à Session à 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)

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_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet




Attacker enables a user to request your server. Example:

<a href="https://yoursite.com/transferMoney?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 GET requests!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)

Overview





• Java Example

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 à look up server state on *every

request*.• Really not good for distributed/clustered apps• Really not good for scale

Overview





• Java Example

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

JSON Web Tokens (JWT)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¯ˉµ€U…8H×

Header

Body (‘Claims’)

Cryptographic Signature


The claims body is the best part! It can tell:

{

"iss":"http://trustyapp.com/",

"exp": 1300819380,

"sub": "users/8983462",

"scope": "self api/buy"

}

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

JSON Web Tokens (JWT)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> jwtClaims = Jwts.parser().setSigningKey(key).parseClaimsJws(jwt);

//OK, we can trust this JWT

} catch (SignatureException e) {

//don't trust the JWT! }

How do you get a Token?

Example: your SPA, your server

1. Token Request

POST /oauth/token HTTP/1.1

Origin: https://foo.com

Content-Type: application/x-www-form-urlencoded

grant_type=password&username=username&password=password

*Assert allowed origin for browser-‐based apps

2. Token Response

HTTP/1.1 200 OK

Content-Type: application/json;charset=UTF-8

Cache-Control: no-store

Pragma: no-cache

{

"access_token":"2YotnFZFEjr1zCsicMWpAA...",

"token_type":"example",

"expires_in":3600,

"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA...",

"example_parameter":"example_value"

}

3. Resource Request

GET /admin HTTP/1.1

Authorization: Bearer 2YotnFZFEjr1zCsicMW...

Example: Token Request using an API Key

POST /token HTTP/1.1

Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&client_id=apiKeyId&client_secret=apiKeySecret

*Assert allowed origin for browser-‐based apps

Thanks!

@afitnerd @goStormpath

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