CLARIN/OAuth2 use case

<sidebar>

• CLARIN web service security
  • CLARIN/Security_for_web_services|Analysis
  • CLARIN/OAuth2|OAuth2
  • CLARIN/OAuth2 use case|OAuth2 use-case
  • CLARIN/OAuth2_real_world_usage|OAuth2 elsewhere
• resources
  • https://mailman.nikhef.nl/mailman/listinfo/biggrid-clarin-security-discuss%7Cmailing list
  • http://agenda.nikhef.nl/conferenceDisplay.py?confId=993%7Cworkshop 2010
  • http://www.clarin.eu/%7CCLARIN
  • http://www.biggrid.nl/%7CBiG Grid

</sidebar> While in the end n-tier delegation is needed withing CLARIN, for the current use-case it is enough to do without real delegation. Plain OAuth2 is sufficient, just to get some experience with it. Delegation can be added later by using a delegation endpoint, or using certificate delegation.

So the goal now is to create a straightforward OAuth2 setup with client, authentication server, and resource server.

This 1-step delegation project has been finalized, resulting in a working demonstrator and implementation by MPI described in the associated report.

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This page contains mostly background information. To get started with the demonstration, please visit the Github repository.

Client

There are many existing OAuth2 clients for various programming languages. Documentation of the settings needed is most important. It would be useful to have a number of examples to use with the most important programming languages (at least Java and PHP). Finally, a way to configure a client with Apache configuration without touching its code, would be a bonus, supplying user and token information in environment variables.

Use-case: CMDI catalog

The CMDI catalog is Java-based using mod_jk. It uses servlet security, with mod_shib for single sign-on. Options:

• client library a Java client library to integrate within the portal for obtaining a token
  • portal needs to be web-based, because obtaining a token requires the user's web browser
• reverse proxy/servlet that always requests an access token after logging into the portal.
  • pro: portal doesn't need to change much / con: token not always needed

The former is cleaner, since it only fetches a token when it is needed. It is probably also easier to implement, and there is quite a number of existing client-side OAuth 2 libraries.

• google-oauth-java-client
• spring-security-oauth
• Apache Amber
• perhaps at some point it would be convenient to write a spring-social provider

Result

This has been achieved using spring-security-oauth.

Authorization server

The OAuth2 AS (authorization server) is the most complex component of the three, which handles user authentication using SAML SSO, consent, possibly some authorization, and token management. It does not need to integrate directly with an existing application (unlike the client or RS). There is not that much choice between existing OAuth2 server implementations currently, and their maturity varies. Options:

• OpenAM OAuth 2 module
• Songkick's OAuth2 provider
  • easy to setup
  • no split AS/RS (no check_token endpoint)
• ndg_oauth_server
  • split AS/RS possible, check_token endpoint present
    • check_token only returns decision, not user identity
  • uses client-certificates for client authentication (instead of http basic auth)
• CloudFoundry User Account and Authentication Server
  • split AS/RS (with check_token endpoint)
  • seems pretty complete

Result

This is currently working with ndg_oauth_server. Open questions or issues:

• Need to implement a resource registry
  • would be nice to specify what attributes to return are allowed per resource
• tokens are currently not bound to a specific resource (=no audience restriction)
• check_token endpoint does not return a user identifier, so we don't know what resource to serve!

Resource server

The resource server needs to verify the access token supplied by the client, and perhaps needs to retrieve user information to base an authorization decision on (since one of the requirements is that resources can make the final decision). This is no more than a simple REST call to a check-token or user-information endpoint on the authentication server.

To make this easy for service developers, at least clear documentation is needed on how to do this. It would be useful to have code samples in a number of programming languages.

To complete it, a way to run the service directly on Apache, with just some extra configuration for doing the check and returning information in (environment) variables, would be great. This may include running a reverse proxy that does the authorization, and passing the request on to the real service upon success.

Use-case: ISOcat

In our use-case, ISOcat is the resource server. While many services use servlet filters for security combined with mod_shib for single sign-on and mod_proxy, ISOcat uses Netkernel. Options would be:

• using a library
  • Apache Amber RS
• servlet-filter (after migration to servlets)
  • RESThub example
  • Protecting resources with OAuth filters for JAX-RS, a RESTful Java API
  • spring-security-oauth (also here)
• reverse proxy that checks the OAuth2 token, optionally fetches user info, and hands it over to the real application
  • Reverse proxy with remote user authorization (mod_perl based)
  • Passing REMOTE_USER from Apache as a reverse proxy to web application servers
• apache module or option that does the same as the proxy directly
  • apache module does not exist, and would be quite some work (not a new idea)
  • if there is an config option to do authentication or set headers from a script, this may be a possibility (something like WSGIAccessScript, or another way of running a script plus mod_setenvif)

The use of a reverse proxy would be the most flexible. If it also integrates well with servlets (which often do use a reverse proxy already), then this would be a fit solution.

Result

This is working using spring security with an adaptation of CloudFoundry's RemoteTokenServices.

Links

• OAuth with Spring Security
• To seek out new life and ...
• Spring Security OAuth2
• Integrating OAuth with AppFuse and its REST API
• OAuth2 without Spring MVC (Spring Forum)
• Installed (desktop) applications
  • at Google