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Before asking OAuthDataProvider to generate a request token, it attempts to validate a callback URI against a Client's application URI.

Finally it delegates to OAuthDataProvider to create a request token, passing to it a populated RequestTokenRegistration bean.

This bean references a Client instance, callback URI and a state. State is something that a consumer may also include during the request token request using a "state" parameter and will be returned back to the consumer alongside the verifier after the request token has been authorized. For example, it may represent a key that a consumer will use to retrieve the state of the request that it was processing when requesting a token. For OAuth 1.0
consumers, the request token itself may represent a good enough key for such purposes, but "state" may need to be used too and will become more useful for OAuth 2.0.

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It's expected that each of the x_oauth_scope values such as "readCalendar" and "updateCalendar" are translated into OAuthPermissions during the creation of a new request token. If no x_oauth_scope parameter is provided then the OAuth data provider will likely assign a default OAuthPermission instance to the new token.

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The consumer is now ready to redirect the current end user to AuthorizationRequestService.

AuthorizationRequestService

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Remember that a third-party consumer redirects the current user to AuthorizationRequestService, for example, here is how a redirection may happen:

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Address: http://localhost:8080/services/social/authorize?oauth_token=6dfd5e52-236c-4939-8df8-a53212f7d2a2
Http-Method: GET
Content-Type: 
Headers: {
Accept=[text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8],   
Referer=[http://localhost:8080/services/forms/reservation.jsp], 
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}

First, AuthorizationRequestService will retrieve RequestToken (which extends the base Token class) from OAuthDataProvider using the value provided by the "oauth_token" query parameter.

Next it uses this token (which also links to Client) to populate an instance of OAuthAuthorizationData bean and returns it. OAuthAuthorizationData contains application name and URI properties, optional list of Permissions and URIs.

Two other important OAuthAuthorizationData properties are "oauthToken" and "authenticityToken", both are important for processing the decision request coming from the authorization form. The former is a request token key which will be used by AuthorizationRequestService to retrieve the RequestToken again and the latter for validating that the current session has not been hijacked - AuthorizationRequestService generates a random key, stores it in a Servlet HTTPSession instance and expects the returned authenticityToken value to match it - this is a recommended approach and it also implies that the authenticityToken value is hidden from a user, for example, it's kept in a 'hidden' form field.

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RequestTokenService will only accept the "oob" value if a client callbackURI property has been set to "oob" during the client application registration process. Specifically, RequestTokenService will expect that a Client bean will have its callbackURI property being set to "oob".

When a callback URI is set to "oob", it means that a user decision response needs to be presented directly to the current user - which will then make the request token and verifier info somehow available to the client application. In case of "oob", AuthorizationRequestService, instead of redirecting the user back to the callback URI as shown earlier on, will simply return an instance of OOBAuthorizationResponse. RequestDispatcherProvider will need to be used for redirecting this data to the view handler exactly how it is done when a user is asked to authorize the client application, with the view handler formatting the data and actually returning it to the user

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Next it asks the data provider to create a new AccessToken based on this RequestToken. The resulting access token key and secret pair is returned back to a consumer:

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Using CXF OAuth service implementations will help a lot with setting up an OAuth server. As you can see from the above sections, these services rely on a custom OAuthDataProvider implementation.

The main task of OAuthDataProvider is to persist request and access tokens and generate authorization/verifier keys. The way it's done is really application-specific. Consider starting with a basic memory based implementation and then move on to keeping the data in some DB.

Note that OAuthDataProvider supports retrieving Client instances but it has no methods for creating or removing Clients. The reason for it is that the process of registering third-party consumers is very specific to a particular OAuth application, so CXF does not offer a registration support service and hence OAuthDataProvider has no Client create/update methods. You will likely need to do something like this:

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When creating RequestToken or AccessToken tokens as well as authorization keys, OAuthDataProvider will need to create unique identifiers.
The way it's done is application specific and custom implementations may also use a utility MD5SequenceGenerator shipped with CXF, for example:

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Finally OAuthDataProvider may need to convert opaque scope values such as "readCalendar" into a list of OAuthPermissions. AuthorizationRequestService and OAuth security filters will depend on it (assuming scopes are used in the first place). In the former case AuthorizationRequestService will use this list to populate OAuthAuthorizationData - the reason this bean only sees Permissions is that the properties OAuthPermission keeps are of no interest to OAuthAuthorizationData handlers.

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Protecting resources with OAuth filters

OAuthRequestFilter request handler can be used to protect the resource server when processing the requests from the third-party consumers. Add it as a jaxrs:provider to the endpoint which deals with the consumers requesting the resources.

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1. It will validate the signature and will get Client and AccessToken from OAuthDataProvider.

2. It will check if AccessToken have a "uris" property set and if yes then it will validate the current request URI against it.

3. If AccessToken has a list of OAuthPermissions. For every permission it will:

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4. Finally, it will create a CXF SecurityContext using this list of OAuthPermissions and the Client loginName property.

This loginName property is something that can be optionally associated with the new Client during the registration - if it is not set then the filter will use a Client "applicationName" property instead. The application code checking the user Principal will see the chosen value. Additionally every OAuthPermission may have a list of application-specific roles such as "consumer", etc, which will be added to SecurityContext and will be checked during SecurityContext.isUserInRole(roleName) calls.

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This SecurityContext will not necessarily be important for some of OAuth applications. Most of the security checks will be done by OAuth filters and security filters protecting the main application path the end users themselves use. Only if you would like to share the same JAX-RS resource code and access URIs between end users and consumers then it can become handy. More on it below.

Note that OAuthServletFilter can be deployed instead. It will need the OAuthDataProvider full class name referenced as an "oauth.data.provider-class" servlet context parameter.

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The injected MessageContext provides an access to OAuthContext which has been set by OAuth filters described in the previous section. OAuthContext will act as a container of the information which can be useful to the custom application code which do not need to deal with the OAuth internals which will likely change between OAuth 1.0 and OAuth 2.0. At the moment OAuthContext provides an access to UserSubject which is created by CXF AuthorizationService at the moment of the end user authorizing the third-party client and captures the end user's login name (and roles which will be available if CXF JAASLoginInterceptor is used to authenticate end users) and associates it with the current RequestToken. It will be a responsibility of custom OAuthDataProviders to make sure this UserSubject bean is copied across to a corresponding AccessToken. OAuthContext also references the list of the permissions which have been validated againt the current client request.

Additionally you may get OAuth filters to set up a SecurityContext which will use the information available in UserSubject, in other words, get the 3rd-party client impersonating the end user (which authorized this client in the first place) for the duration of the current request. Set a jaxrs contextual "org.apache.cxf.rs.security.oauth.use_user_subject" property to 'true' for this to happen.

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When developing a third party application which needs to participate in OAuth flows one has to write the code that will redirect users to OAuth AuthorizationRequestService, interact with RequestTokenService and AccessTokenService in order to get request and access tokens as well as correctly build Authorization OAuth headers when accessing the end users' resources. JAX-RS makes it straightforward to support the redirection, while OAuthClientUtils class makes it possible to encapsulate most of the complexity away from the client application code.

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Also note that AuthorizationRequestService can return XML or JSON OAuthAuthorizationData representations. That makes it easy for a client code to get OAuthAuthorizationData and offer a pop-up window or get the input from the command-line. Authorizing the third-party application might even be automated in this case - which can lead to a complete 3-leg OAuth flow implemented without a human user being involved.

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As noted above, Client, AccessToken (in its Token superclass) and OAuthPermission all have an optional URIs property. Thus one way to solve the problem with the private calendar is to add, say, a uri "/calendar/{id}" or "/calendar/1" (etc) property to OAuthPermission (representing a scope like "readCalendar") and the OAuth filter will make sure no subresources beyond "/calendar/{id}" can be accessed. Note, adding a "*" at the end of a given URI property, for example, "/a*" will let the consumer to access "/a", "/a/b", etc.

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