Secure Your REST API

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Les Hazlewood, Stormpath CTO, already showed you how to build a Beautiful REST+JSON API, but how do you secure your API? At Stormpath, we spent 18 months researching best practices. Join Les as he explains how to secure your REST API, the right way. We'll also host a live Q&A session at the end.

Les will cover:
OAuth2
OAuth Access Tokens
Scoping for Permissions
JWTs
Using JWTs as tokens
Securing JWTs
Authentication, Authorization, and More!

Transcript

1. REST API Security Les Hazlewood @lhazlewood PMC Chair, Apache Shiro Expert Group Member, JEE Application Security (JSR-375) Founder & CTO, Stormpath
2. About Stormpath • User Management API for Developers • Password security • Authentication and Authorization • Multi Tenancy • MFA, SAML, OAuth2 • LDAP & Active Directory Cloud Sync • Instant-on, scalable, and highly available • Free for developers ...
3. Overview • HTTP Authentication • HTTP Authentication Schemes Comparison • API Key Authentication • Token Authentication • Authorization
4. REST API Focus • Eliminate server state • Secure user credentials • Secure server endpoints • Expose access control rules • SPAs and Mobile: ‘Untrusted Clients’
5. HTTP(S) Authentication & Authorization
6. Authentication Proving you are who you say you are.
7. Authorization Ensuring someone is allowed to do what they are trying to do.
8. HTTP Authentication & Authorization • Authorization header • No Custom Headers! • Stay spec-standard • No pre-flight CORS requests (browsers) req’d • Custom schemes easily supported
9. Authorization header How does it work?
10. Authorization header How does it work? Challenge Response protocol
11. 1. Request GET /admin HTTP/1.1
12. 2. Challenge HTTP/1.1 401 Unauthorized WWW-Authenticate: scheme-name <stuff> *multiple schemes allowed, typically set as multiple WWW-Authenticate headers
13. 3. Re-Request GET /admin HTTP/1.1 Authorization: scheme-name <stuff>
14. Example: HTTP Basic Authentication
15. 1. Request (Basic) GET /admin HTTP/1.1
16. 2. Challenge (Basic) HTTP/1.1 401 Unauthorized WWW-Authenticate: Basic realm=“MyApp”
17. 3. Re-Request (Basic) GET /admin HTTP/1.1 Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
18. Schemes • Basic • Digest Schemes (OAuth 1.0a) • Bearer Token Schemes (OAuth2) • Custom
19. HTTP Basic
20. HTTP Basic String value = username + ‘:’ + raw_password String schemeValue = base64_encode(value) ... GET /admin HTTP/1.1 Authorization: Basic schemeValue
21. HTTP Basic Pros: • Very easy to use • Supported by everything Cons: • Raw password always transmitted • Easy to leak raw password if not careful (logging) • Susceptible to Man-In-The-Middle attacks • HTTPS *always* required • Client must constantly retain/reference the raw password (server clients usually ok, browser clients not ok)
22. Digest Schemes
23. Digest Schemes: Client request.headers[‘Client-Id’] = getMyId() String digest = hmacSha256(request, password) request.headers[‘Authorization’] = ‘Foo ‘ + digest send(request)
24. Digest Schemes: Server String clientId = request.headers[‘Client-Id’] byte[] password = lookupPassword(clientId); String serverComputedDigest = hmacSha256(request, password) String val = request.headers[‘Authorization’] String clientSpecifiedDigest = val.remove(‘Foo ‘) if (clientSpecifiedDigest != serverComputedDigest) { sendError(401, response) return } //otherwise request is authenticated
25. Digest Schemes: OAuth 1.0a example Authorization: OAuth realm="http://sp.example.com/", oauth_consumer_key="0685bd9184jfhq22”, oauth_token="ad180jjd733klru7", oauth_signature_method="HMAC-SHA1", oauth_signature="wOJIO9A2W5mFwDgiDvZbTSMK%2FPY%3D", oauth_timestamp="137131200", oauth_nonce="4572616e48616d6d65724c61686176”
26. Digest Schemes Pros: • Probably most secure • Password never sent over the wire • HTTPS not required (but your data may still require HTTPS) • Can guarantee end-to-end HTTP message authenticity (HTTPS cannot do this) • Not susceptible to Man-In-The-Middle attacks Cons: • Very difficult to design safely • Difficult to understand and use • Difficult to implement libraries • Client needs to retain a constant reference to the password (server clients usually ok, browser clients maybe not?)
27. Bearer Token Schemes
28. Bearer Token Schemes Authorization: Bearer opaque-token
29. Bearer Token Schemes opaque-token can be whatever you want*
30. Bearer Token Schemes opaque-token can be whatever you want* *should always be cryptographically-signed and expire
31. Bearer Token Schemes: OAuth 2 Example Authorization: Bearer eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJpc3 MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0d HA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ.dBjft JeZ4CVP-92K27uhbUJU1p1r_wW1gFWFOEjXk
32. Bearer Token Schemes Pros: • Easier to use than digest • De-facto standard token format (JWT) • Can contain state – no server sessions needed • Does not require constant access to the user password Cons: • HTTPS always required, during and always after login (not a big deal nowadays) • Cannot guarantee end-to-end HTTP message authenticity (like digest schemes can) • Susceptible to Man-In-The-Middle attacks • Token creation and renewal workflows can be very complicated and confusing depending on use case (OAuth2 confuses many people). • When used for Browser or Mobile, additional security still required (Origin checks, CSRF- protection, etc) • Token content is not standard – applications can open themselves to attack
33. Bearer Token Schemes: Session IDs? Session ID cookies are a type of bearer token! Set-Cookie: session=dhj7Wkx8fj; secure; HttpOnly Notes: - Same ‘Cons’ as previous slide - Require server state L - Susceptible to CSRF attacks L - Opaque – no meaning for rich clients (SPA, mobile) L - Service Architectures might need a centralized ID de-referencing service L - Can set the secure and HttpOnly flags J - JWTs are better, as we’ll soon see.
34. Custom Scheme
35. Custom Scheme • Only if you really, Really, REALLY know what you’re doing. Seriously. No, rly. Srsly. • Non-standard, so you essentially must provide your own client libraries.
36. Custom Scheme • Stormpath has a custom SAUTHC1 digest scheme • Authenticates the entire HTTP Message, including the Body (OAuth 1.0a does not) • Uses nonces to prevent replay attacks • Uses key derivation algorithms and HMAC-SHA-256 • We use it for our own SDKs* • If you’re curious: https://github.com/stormpath (search for ‘sauthc1’ in any stormpath-sdk-* project) *Basic still supported for non-SDK clients or ‘weird’ environments
37. API Key Authentication
38. API Key Example ID : YLNVXG091ZO1BSANZ5U6DCTIX Secret: ZediwUeDCNl13ldjaFKFQzz0eD13PO931DLAopdeywixaeUAhsip+92iaY
39. API Keys • Entropy • Password Independent • Scope • Speed • Limited Exposure • Traceability
40. API Keys • Can be thought of as a really long username and password pair. • Can be used with any HTTP Authentication Scheme that accepts a username and password: Basic, Digest, OAuth2, etc. • Almost exclusively used for server-to-server communication. • Never embed API Key secrets in untrusted clients like JavaScript or mobile applications.
41. HTTP Basic with API Key String value = apiKeyId + ‘:’ + apiKeySecret String schemeValue = base64_encode(value) ... GET /admin HTTP/1.1 Authorization: Basic schemeValue
42. Token Authentication
43. Why not just use Session IDs?
44. 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
45. 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. • Susceptible to CSRF attacks
46. 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
47. Token Authentication to the rescue!
48. How do you get a Token?
49. Example: your SPA, your server
50. 1. Token Request POST /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
51. 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” }
52. 3. Resource Request GET /admin HTTP/1.1 Authorization: Bearer 2YotnFZFEjr1zCsicMWpAA
53. 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=apiKeyS ecret *Assert allowed origin for browser-based apps
54. How does the server create a Token?
55. 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.
56. JSON Web Tokens (JWT) • You can store them in cookies! But all those cookie security rules still apply (CSRF protection, etc). • You can entirely replace your session ID with a JWT.
57. JSON Web Tokens (JWT) In the wild they look like just another ugly string: eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJ pc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQo gImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnV lfQ.dBjftJeZ4CVPmB92K27uhbUJU1p1r_wW1gFWFOEj Xk
58. JSON Web Tokens (JWT) But they do have a three part structure. Each part is a Base64Url-encoded string: eyJ0eXAiOiJKV1QiLA0KICJhb GciOiJIUzI1NiJ9 . eyJpc3MiOiJqb2UiLA0KICJle HAiOjEzMDA4MTkzODAsDQogIm h0dHA6Ly9leGFtcGxlLmNvbS9 pc19yb290Ijp0cnVlfQ . dBjftJeZ4CVPmB92K27uhbUJU 1p1r_wW1gFWFOEjXk Header Body (‘Claims’) Cryptographic Signature
59. JSON Web Tokens (JWT) Base64Url-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
60. JSON Web Tokens (JWT) 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
61. JSON Web Tokens (JWT) 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 When it expires
62. JSON Web Tokens (JWT) 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 When it expires Who it represents
63. JSON Web Tokens (JWT) 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 When it expires Who it represents What they can do
64. 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
65. JSON Web Tokens (JWT) 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!
66. Authorization
67. Authorization • JWT Claims can have whatever you want • Use a scope field that contains a list of permissions for that user • Client can inspect the claims and scope and turn on or off features based on permissions* • *Server must always assert permissions
68. Authorization Failed: 403 HTTP/1.1 403 Forbidden
69. How do you do it on the JVM? JJWT is awesome https://github.com/jwtk/jjwt
70. How do you do it on the JVM? 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:
71. How do you do it on the JVM? 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! }
72. In addition to user authentication and data security, Stormpath can handle authentication and authorization for your API, SPA or mobile app. • API Authentication • API Key Management • Authorization • Token Based Authentication • OAuth • JWTs • MFA, SAML, OAuth2 • Multi-Tenancy http://docs.stormpath.com/guides/api-key-management/ Implementations in your Library of choice: https://docs.stormpath.com/home/ Use Stormpath for API Authentication & Security
73. Follow Us on Twitter @lhazlewood @goStormpath