Authentication - Framework

The core piece of functionality with respect to authentication in Sling is contained in the Sling Auth Core bundle. This bundle provides the API for Sling and Sling applications to make use of authentication.

This support encompasses three parts:

• The AuthenticationSupport service provided by the SlingAuthenticator class. This service can be used by implementations of the OSGi HttpContext interface to delegate authentication.
• The Authenticator service also provided by the SlingAuthenticator class. This service may be used by Sling applications to help clients login and logout.
• The AuthenticationHandler service interface. These services may be implemented by extensions to support various ways for transporting credentials from clients to the Sling server.

This page describes how the SlingAuthenticator class provides the AuthenticationSupport and Authenticator services. For a description of the AuthenticationHandler service interface and the interaction between the SlingAuthenticator and the AuthenticationHandler services refer to the AuthenticationHandler page.

The SlingAuthenticator class is an internal class of the org.apache.sling.auth.core bundle and implements the Authenticator and AuthenticationSupport services.

The API mentioned in this document and its implementation is part of the Apache Sling Auth Core bundle.

AuthenticationSupport

The AuthenticationSupport service interface defines a single method: handleSecurity. This method is intended to be called by the handleSecurity method of any HttpContext implementation wishing to make use of the Sling Authentication Framework.

The Sling Authenticator implementation selects an AuthenticationHandler service appropriate for the request and calls the AuthenticationHandler.extractCredentials method to extract the credentials from the request. If no credentials could be extracted, the Sling Authenticator either admits the request as an anonymous request or requests authentication from the client by calling its own login method.

The implementation follows this algorithm:

1. Select one or more AuthenticationHandler for the request according to the request URL's scheme and authorization part.
2. Call the extractCredentials method of each authentication handler, where the order of handler call is defined by the length of the registered path: handlers registered with longer paths are called before handlers with shorter paths. The goal is to call the handlers in order from longest request path match to shortest match. Handlers not matching the request path at all are not called.
3. The first handler returning a non-null AuthenticationInfo result "wins" and the result is used for authentication.
4. If any AuthenticationInfoPostProcessor services are registered, the AuthenticationInfo object is passed to their postProcess() method.
5. If no handler returns a non-null result, the request may be handled anonymously. In these cases, an empty AuthenticationInfo object is passed to any AuthenticationInfoPostProcessor services.
6. (Try to) log into the repository either with the provided credentials or anonymously.
7. If there were credentials provided and the login was successful, a login event is posted if the AuthenticationInfo object contains a non-null object with the key $$auth.info.login$$ (AuthConstants.AUTH_INFO_LOGIN). This event is posted with the topic org/apache/sling/auth/core/Authenticator/LOGIN. (added in Sling Auth Core 1.1.0)
8. Set request attributes listed below.

Extracting the credentials and trying to login to the repository may yield the following results:

Request Attributes on Successful Login

The handleSecurity method gets credentials from the AuthenticationHandler and logs into the JCR repository using those credentials. If the login is successful, the SlingAuthenticator sets the following request attributes:

NOTE: Do NOT use the javax.jcr.Session request attribute in your Sling applications. This attribute must be considered implementation specific to convey the JCR Session to the SlingMainServlet. In future versions of the Sling Auth Core bundle, this request attribute will not be present anymore. To get the JCR Session for the current request adapt the request's resource resolver to a JCR Session:

Session session = request.getResourceResolver().adaptTo(Session.class);

Anonymous Login

The SlingAuthenticator provides high level of control with respect to allowing anonymous requests or requiring authentication up front:

• Global setting of whether anonymous requests are allowed or not. This is the boolean value of the Allow Anonymous Access (auth.annonymous) property of the SlingAuthenticator configuration. This property is supported for backwards compatibility and defaults to true (allowing anonymous access). Setting it to true is a shortcut for setting sling.auth.requirements to -/.
• Specific configuration per URL. The Authentication Requirements (sling.auth.requirements) property of the SlingAuthenticator configuration may provide a list of URLs for which authentication may be required or not: Any entry prefixed with a dash - defines a request path prefix for which authentication is not required. Any entry not prefixed with a dash or prefixed with a plus + defines a subtree for which authentication is required up front and thus anonymous access is not allowed. This list is empty by default.
• Any OSGi service may provide a sling.auth.requirements registration property which is used to dynamically extend the authentication requirements from the Authentication Requirements configuration. This may for example be set by AuthenticationHandler implementations providing a login form to ensure access to the login form does not require authentication. The value of this property is a single string, an array of strings or a Collection of strings and is formatted in the same way as the Authentication Requirements configuration property.

The values set on the Authentication Requirements configuration property or the sling.auth.requirements service registration property can be absolute paths or URLs like the path service registration property of AuthenticationHandler services. This allows the limitation of this setup to certain requests by scheme and/or virtual host address. The requests path (HttpServletRequest.getServletPath() + HttpServletRequest.getPathInfo()) is afterwards matched against the given paths. It matches if it starts with one of the given paths.

Examples

• The LoginServlet contained in the Sling Auth Core bundle registers itself with the service registration property sling.auth.requirements = "-/system/sling/login" to ensure the servlet can be accessed without requiring authentication (checks for slash or dot or end of string). The following request urls would work then without authentication:
  • /system/sling/login
  • /system/sling/login.html
  • /system/sling/login/somesuffix

While the following request will still require authentication

* /system/sling/login-test 

• An authentication handler may register itself with the service registration property sling.auth.requirements = "-/apps/sample/loginform" to ensure the login form can be rendered without requiring authentication.

Authenticator implementation

The implementation of the Authenticator interface is similar for both methods:

login

1. Select one or more AuthenticationHandler for the request according to the request URL's scheme and authorization part.
2. Call the requestCredentials method of each authentication handler, where the order of handler call is defined by the length of the registered path: handlers registered with longer paths are called before handlers with shorter paths. The goal is to call the handlers in order from longest request path match to shortest match. Handlers not matching the request path at all are not called.
3. As soon as the first handlers returns true, the process ends and it is assumed credentials have been requested from the client.

The login method has three possible exit states:

logout

1. Select one or more AuthenticationHandler for the request according to the request URL's scheme and authorization part.
2. Call the dropCredentials method of each authentication handler, where the order of handler call is defined by the length of the registered path: handlers registered with longer paths are called before handlers with shorter paths. The goal is to call the handlers in order from longest request path match to shortest match. Handlers not matching the request path at all are not called.

Unlike for the login method in the logout method case all AuthenticationHandler services selected in the first step are called. If none can be selected or none can actually handle the dropCredentials request, the logout silently returns.