- Generated on Thu Nov 9 2017 18:10:41 for VAL by
1.8.14
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VAL
Virtuoso Authentication Layer
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VAL provides the means to easily add authentication and ACL support to existing or new vsp-based applications. This tutorial shows the three main steps to add authentication and ACL protection to an application. We are using curi - the Compressed URI Service as an example.
For curi we want to add login information, a means for the user to logout, and ACLs to protect the service.
The first and simplest step is to check if the user already provided authentication information as supported by VAL. This can simply be achieved by calling VAL.DBA.get_authentication_details_for_connection() at the top of the vsp page:
realm parameter and only return authentication data for the given realm. Additionally it will honor the app_realm setting in the virtual dir serving the page in question. Thus, there are basically two ways to define the realm for an application: 1. Set it in the virtual dir, and 2. Force it manually via the realm parameter.After the call to VAL.DBA.get_authentication_details_for_connection() the application can use the information. The most important one is the value of val_serviceId which defines who is authenticated. If it is null then the user has not authenticated yet.
VAL provides an authentication and a logout page to support the most simple login and logout links possible. Given that the application page is stored in pageUrl the following links can be used:
However, in our case a dedicated login page is more desirable since it allows to configure certain aspects of authenticate.vsp. Thus, we create a new page login.vsp with the following content (or at least parts of it):
The settings should be obvious:
__val_auth_page__ We tell authenticate.vsp to use login.vsp instead of its own URL for all login links.__val_req_res_label__ A custom label for the login dialog to tell the user which service they log into.__val_oauth_scope__ The optional OAuth scope to use (basic, profile, or dav). This is only of interest for applications that reuse the created OAuth sessions for additional API calls to the 3rd-party service.So we end up with code for creating a login/logout box like the following:
Once the user authenticates, they will be redirected to the pageUrl with a newly created sid cookie. the logout page will remove that cookie.
Tip: A slightly nicer logged in message with link can be created with code like the following which makes use of the two utility procedures VAL.DBA.get_profile_url() and VAL.DBA.get_profile_name():
A typical situation for authentication-enabled applications is forcing the user to authenticate. Ideally this is done via 40x page options in the virtual directory in combination with VAL's authenticate.vsp page (which is also used for login links). One simply creates a new file 40x.vsp which has the following content:
authenticate.vsp can be configured via a set of connection settings:
__val_req_res__ The resource which is protected, ie which requires the login. This is only used to retrieve ownership information for the "request access" dialog that authenticate.vsp will show if access was denied. This will default to the returnto URL if not provided, and should that also be null (as is the case if authenticate.vsp is used as 40x_page) then the requested URL will be used.__val_req_acl_scope__ The ACL scope in which the above resource is protected. This is only used to retrieve ownership information for the "request access" dialog that authenticate.vsp will show if access was denied. If not given, then no "request access" dialog is shown.__val_req_res_label__ An optional label for the login dialog showing the user for which service they are authenticating.__val_auth_page__ We tell authenticate.vsp to use our custom page login.vsp instead of its own URL for all login links.val_err_msg An error message indicating any kind of error. This should be set to http_param ('error.msg') for the simple reason that Virtuoso does clear the http params before processing the 40x page.This page will be used as 40x page in the virtual directory configuration:
Then the application can raise a permission denied error as shown in the following example:
If val_serviceId is null then the user has not logged in and the application simply requests that they do. Otherwise 403 indicates that permission was denied to the authenticate user. The authenticated has to be communicated to authenticate.vsp via the __val_denied_service_id__ connection setting.
In 40x Pages we saw how to use authenticate.vsp as a 40x_page. Now we will add ACL protection to the curi service and put the new 40x_page to use.
We want to be able to grant people the right to create new compressed URIs and others the right to read these. To that end we define a new scope urn:virtuoso:val:scopes:curi which is only used for curi and a virtual resource URI which is used to grant permissions: urn:virtuoso:access:curi These URIs are arbitrary, they simply follow a random scheme to be easily recognizable. In theory they could be any URI one wanted to use.
VAL makes use of scope definitions to get default access modes for disabled scopes (the default). Thus we start by defining our new scope in the corresponding VAL acl schema graph (Hint: standard scopes for DAV, etc. are defined in the OpenLink ACL ontology, example: oplacl:Dav):
The most important part is oplacl:hasDefaultAccess which defines the access modes used in case ACL evaluation has not been enabled for the curi scope. In this case everyone is allowed to create and read compressed URIs.
Now at the top of the create.vsp page which allows to create new compressed URIs we add the following ACL check (after the code from 40x Pages):
Some of this code we already know from before. But the big first part is new. First we check if we are logged in as an admin user. VAL provides us with the convinience procedure VAL.DBA.is_admin_user() for that. Of course only "real" users, ie. SQL users, can be administrators of the V instance. In case no admin credentials were provided we continue with the ACL check using VAL.DBA.check_access_mode_for_resource() which allows to check for exactly one mode on one resource for one service id. Here we use all the details that were provided by VAL.DBA.get_authentication_details_for_connection() and combine them with the resource and scope URIs we defined above.
Since we want to create a compressed URI we use the oplacl:Write access mode. Should no ACL exist which grants access we continue to raise a 40x error. But before we do that we set two more variables:
__val_denied_service_id__ This is important as it allows authenticate.vsp to know that access has been denied to a certain person and the user should be asked to login again. Without this setting, authenticate.vsp would simply return to the returnto URL if authentication information could be found. This would result in an endless loop. Should no authentication information exist yet then authenticate.vsp will simply ask for it.__val_req_acl_mode__ Like the resource and the scope settings above the mode is only used for the "request access" dialog. It allows authenticate.vsp to create a more detailed access request message to the resource owner.Finally we add the same code to the get.vsp page which handles the conversion of comressed to uncompressed URIs. The only difference is the access mode:
authenticate.vsp provides a simple dialog through which users can request access to a certain resource, should it have been denied. This dialog is shown by authenticate.vsp if the following conditions hold true:
__val_denied_service_id__ is non-null (See 40x Pages for details).__val_req_res__ has to be non-null and an owner has to be set (DAV resources are handled as special cases, for every other resource see VAL.DBA.set_resource_ownership(), VAL.DBA.add_ownership_graph() and friends.)Once these conditions are fulfilled then the user has the option to write a message to the owner of the resource, requesting to grant them access.
In the case of curi the vsp pages are not executed as dba but using the dedicated account CURI which improves security and is generally recommended. However, since most of the internal VAL API procedures require special permissions this user needs to be granted the VAL_AUTH and VAL_ACL roles to be able to execute:
(The API documentation contains hints about which role grants the right to execute a specific procedure in said procedure's documentation.)
As explained in SPARQL ACL Rules - Defining access to private graphs VAL handles SPARQL ACL rules as a special case, using the fixed rule scope oplacl:PrivateGraphsScope (VAL.DBA.get_sparql_scope()) and a graph security callback. The following example shows how all the different pieces of VAL can be used to perform ACL-protected SPARQL queries (as done by sparql.vsp).
Imagine the actual SPARQL query is stored in variable query.
First we get the authentication information for the current connection. It is important to set val_realm to null because it is an inout variable which has to be tested against null in the procedure.
We use sid as name for the cookie which stored the session id. This is the default but can be set to any value required. (However, be aware that authenticate.vsp currently does not allow to change this.)
After the call to VAL.DBA.get_authentication_details_for_connection() we know if a user is logged in or not and can act accordingly. One might either want to show a login link or simply proceed to execute the query as user nobody (which means that only public ACL rules apply).
As recommended we execute the query as user VAL_SPARQL_ADMIN to get full access to the entire triple store. We then use the callback to restrict that access according to the ACL rules setup in the current realm. We do not use dba for security reasons. VAL_SPARQL_ADMIN is a special user which has full access to all public and private graphs. The permissions reported by the callback include not only the implied permissions set by VAL ACL rules, but also the physical graph permissions set by RDF_USER_PERMS_SET.
Finally we can execute the query and clear the temporary WebID graph:
1.8.14