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When and Why Would I use Oauth2?
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When and Why Would I use Oauth2?


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Slides from SpringOne 2012 ( …

Slides from SpringOne 2012 (

One of the questions we get asked the most by developers and architects is: when and why would I use OAuth2? The answer, as often with such questions, is “it depends”, but there are some features of OAuth2 that make it compelling in some situations, especially in systems composed of many lightweight web services, which becoming a very common architectural pattern.

This presentation will not go into a lot of detail about the OAuth2 protocol and related specifications, but will attempt to show some of the key features of a system secured with OAuth2 and the decision points when choosing to build such a system.

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  • 1. OAuth2 and REST Securing REST-ful Web Services with OAuth2 Dave Syer, 2012 Twitter: @david_syer Email: Agenda Why would I use OAuth2? If I was going to use Spring how would that look? Whats the easiest way to get something working? Blog: Introduction There is a strong trend distributed systems with lightweight architectures So what are people doing about security in such systems? What is a Lightweight Service? HTTP transport. Text-based message content, usually JSON. Small, compact messages, and quick responses. REST-ful, or at least inspired by the REST Some degree of statelessness Interoperability. What Are the Security Requirements Identity and permissions: how is identity and permission information conveyed to a service? how is it decoded and interpreted? what data are needed to make the access decision (user accounts, roles, ACLs etc.)? how is the data managed: who is responsible for storing and retrieving it? HTTP Basic Authentication something of a lowest common denominator supported on practically all servers natively and out of the box ubiquitous support on the client side in all languages Example:1 of 10 17/10/12 05:40
  • 2. OAuth2 and REST $ curl "https://$username:$password@myhost/resource" So whats wrong with that? Nothing, but... Where do you get the credentials (the username and password)? Fine for systems where all participants can share secrets securely In practice that means small systems Only supports username/password Only covers authentication User or Client Permissions Finer-grained information about the authenticated party Role-based access: very common, sometimes available in server/container Need to categorize user accounts, e.g. USER and ADMIN Often business requirements are more complex Identity Management: Three Corners Identity Management: Four Corners2 of 10 17/10/12 05:40
  • 3. OAuth2 and REST Centralized Identity Management Centralized Identity Management Centralized: scales better than peers sharing secrets Peer-to-peer: N(N-1)/2 pairs Centralized: N pairs For user accounts the scalability benefit is even bigger OAuth2 Centralizing accounts and secrets is great, but what about permissions?3 of 10 17/10/12 05:40
  • 4. OAuth2 and REST OAuth 2.0 adds an extra dimension - more information for the access decision Standards always help in security Lightweight - easy to curl Requires HTTPS for secure operation, but you can test with HTTP Quick Introduction to OAuth2 A Client application, often web application, acts on behalf of a User, but with the Users approval Authorization Server Resource Server Client application Common examples of Authorization Servers on the internet: Facebook - Graph API Google - Google APIs Cloud Foundry - Cloud Controller Typical Web Application Client OAuth2 and the Lightweight Service Example command line Client: $ curl -H "Authorization: Bearer $TOKEN" https://myhost/resource is a Resource Server https://myhost TOKENis a Bearer Token it came from an Authorization Server Role of Client Application Register with Authorization Server (get a client_id and maybe a client_secret) Do not collect user credentials Obtain a token (opaque) from Authorization Server On its own behalf - client_credentials On behalf of a user4 of 10 17/10/12 05:40
  • 5. OAuth2 and REST Use it to access Resource Server Obtaining a Client Credentials Token A client can act in its own right (not on behalf of a user): $ curl "" -d grant_type=client_credentials -d client_id=myclient Result: { access_token: FUYGKRWFG.jhdfgair7fylzshjg.o98q47tgh.fljgh, expires_in: 43200, client_id: myclient, scope: uaa.admin } OAuth2 Key Features Extremely simple for clients Access tokens carry information (beyond identity) Resource Servers are free to interpret tokens Example token contents: Client id Resource id (audience) User id Role assignments UAA Bearer Tokens OAuth 2.0 tokens are opaque to clients But they carry important information to Resource Servers Example of implementation (from Cloud Foundry UAA, JWT = signed, base64-encoded, JSON): { "client_id":"vmc", "exp":1346325625, "scope":["","openid","password.write"], "aud":["openid","cloud_controller","password"], "user_name":"", "user_id":"52147673-9d60-4674-a6d9-225b94d7a64e", "email":"", "jti":"f724ae9a-7c6f-41f2-9c4a-526cea84e614" } Web Application Client Again The Client wants to access a Resource on behalf of the User5 of 10 17/10/12 05:40
  • 6. OAuth2 and REST Obtaining a User Token A client can act on behalf of a user (e.g. authorization_code grant): Authorization Code Grant Summary 1. Authorization Server authenticates the User 2. Client starts the authorization flow and obtain Users approval 3. Authorization Server issues an authorization code (opaque one-time token) 4. Client exchanges the authorization code for an access token. Role of Resource Server6 of 10 17/10/12 05:40
  • 7. OAuth2 and REST 1. Extract token from request and decode it 2. Make access control decision Scope Audience User account information (id, roles etc.) Client information (id, roles etc.) 3. Send 403 (FORBIDDEN) if token not sufficient Role of the Authorization Server 1. Grant tokens 2. Interface for users to confirm that they authorize the Client to act on their behalf 3. Authenticate users (/authorize) 4. Authenticate clients (/token) #1 and #4 are covered thoroughly by the spec; #2 and #3 not (for good reasons). Client Registration and Scopes For secure channels a client has to authenticate itself to obtain a token, so it has to be known to the Authorization Server. Registration provides at a mimimum: authentication (shared secret) registered redirect URI (optional but essential to prevent attacks) allowed scopes (clients are not permitted access to all resources) Also useful: a way to identify which resources can be accessed ownership information (which user registered the client) More on Scopes Per the spec they are arbitrary strings. The Authorization Server and the Resource Servers agree on the content and meanings. Examples: Google: Facebook: email, read_stream, write_stream UAA:, cloud_controller.write,, openid Authorization Server has to decide whether to grant a token to a given client and user based on the requested scope (if any). UAA Scopes UAA scopes are actually Groups in the User accounts GET /Groups, Get /Users/{id} { "id": "73ba999e-fc34-49eb-ac26-dc8be52c1d82", "meta": {...}, "userName": "marissa", "groups": [ ... { "value": "23a71835-c7ce-43ac-b511-c84d3ae8e788", "display": "uaa.user", "membershipType": "DIRECT" } ], } Special Mention for Vmc7 of 10 17/10/12 05:40
  • 8. OAuth2 and REST The UAA authenticates requests from vmc in a special way: $ curl -d response_type=token -d client_id=vmc -d -d source=credentials -d username=$username -d password=$password Result: 302 FOUND ... Location: Authentication and the Authorization Server Authentication (checking user credentials) is orthogonal to authorization (granting tokens) They dont have to be handled in the same component of a large system Authentication is often deferred to existing systems (SSO) Authorization Server has to be able to authenticate the OAuth endpoints ( /authorize and /token) It does not have to collect credentials (except for grant_type=password) Cloud Foundry UAA Authorization Server Cloud Foundry Login Server8 of 10 17/10/12 05:40
  • 9. OAuth2 and REST Role of Login Server Authenticate users and collect user approvals for OAuth2 scopes Send authenticated user info in trusted channel to UAA Maintain SSO state (e.g. session cookie) Branded UI OAuth2 endpoints - delegate (pass through) to UAA Cloud Foundry UAA as a General Purpose Solution User Account and Authentication Service is part of Cloud Foundry open source and fairly generic sample apps (including login server) wrapper for Spring Security OAuth runs in a servlet container (e.g. tomcat) easy for Spring developers to install and customize look for UAA blogs at (and .com) UAA OAuth Implementation UAA makes some explicit choices where the spec allows it, and also adds some useful features: Client registration validation, e.g. implicit has no secret Client has separate allowed scopes for user tokens and client tokens (if allowed). User account management: groups = scopes, period-separated JWT tokens, signed but not encoded, includes audience (a.k.a. resource_id) /userinfo endpoint for remote authentication (SSO) Auto-approve for client apps that are part of platform Special authentication channels for /authorize: source=credentials - used by vmc source=login - used by Login Server (Login Server) autologin via code=... UAA Resources (Endpoints) Brief list of all the UAA endpoints (with valid scopes if it is an OAuth2 resource):9 of 10 17/10/12 05:40
  • 10. OAuth2 and REST OAuth2 Authorization Server: oauth/authorize and /oauth/token User info endpoint (for SSO): /userinfo, scope openid Token decoding endpoint: /check_token Login info endpoint (open to anyone): /login SCIM user account management: /Users, scopes [, scim.write]. Password changes: /Users/{id}/password, scope password.write UAA Resources (continued) Token management, e.g. cancelling an approval: /oauth/users/{id}/tokens and /oauth/clients/{id}/tokens, scopes [, tokens.write] Client registration: /oauth/clients, scopes [, clients.write, clients.secret] Password strength meter: /password Management endpoints, used by the Cloud Foundry platform internally: /health and /varz Alternatives to OAuth2 OAuth 1.0a SAML Custom solution, e.g. HMAC signed requests Extensions to OAuth2 In Conclusion Lightweight services demand lightweight infrastructure Security is important, but should be unobtrusive OAuth 2.0 is a standard, and has a lot of useful features Spring Security OAuth aims to be a complete solution at the framework level Cloud Foundry UAA adds some implementation details and makes some concrete choices Links http://blog.springsource.org10 of 10 17/10/12 05:40