UA Part 3: Address Space Model

A Role is a function assumed by a Client when it accesses a Server. Roles are used to separate authentication (determining who a Client is) from authorization (determining what the Client is allowed to do). By separating these tasks Servers can allow centralized services to manage user identities and credentials while the Server only manages the Permissions on its Nodes assigned to Roles.

The set of Roles supported by a Server are published as components of the RoleSet Object defined in OPC 10000-18. Servers should define a base set of Roles and allow configuration Clients to add system specific Roles. Adding, deleting, and modifying Roles is restricted to callers with appropriate permissions.

When a Session is created,or a Session-less Service is called, the Server must determine what Roles are granted to that Session or Session-less Service invocation. This specification defines standard mapping rules which Servers may support. Servers may also use vendor specific mapping rules in addition to or instead of the standard rules.

The Anonymous Role is the default Role which is always assigned to all Sessions.

The AuthenticatedUser Role is always assigned when a Session has been authenticated with a UserIdentityToken other than the AnonymousIdentityToken (see OPC 10000-4).

The standard mapping rules allow Roles to be granted based on:

User identity;
Application identity;
Endpoint;

User identity mappings can be based on user names, user certificates or user groups.

Application identity mappings are based on the ApplicationUri specified in the Client Certificate. Application identity can only be enforced if the Client proves possession of a trusted Certificate by using it to create a Secure Channel or by providing a signature in ActivateSession (see OPC 10000-4).

Endpoint identity mappings are based on the URL used to connect to the Server. Endpoint identity can be used to restrict access to Clients running on particular networks. Endpoint identity mappings should not be used as the only criteria unless access to the endpoint is restricted by the network infrastructure. For example, an endpoint on a loopback address is only accessible from the same machine.

OPC 10000-5 defines the Objects, Methods and DataTypes used to represent and manage these mapping rules in the Address Space.

4.9.2 Well Known Roles

The NodeIds for the well-known Roles are defined in OPC 10000-6. All Servers should support the well-known Roles which are defined in Table 2.

Table 2 – Well-Known Roles

BrowseName	Suggested Permissions
Anonymous	The Role is allowed to browse and read non-security related Nodes only in the Server Object and all type Nodes.
AuthenticatedUser	The Role is allowed to browse and read non-security related Nodes.
Observer	The Role is allowed to browse, read live data, read historical data/events or subscribe to data/events.
Operator	The Role is allowed to browse, read live data, read historical data/events or subscribe to data/events. In addition, the Session is allowed to write some live data and call some Methods.
Engineer	The Role is allowed to browse, read/write configuration data, read historical data/events, call Methods or subscribe to data/events.
Supervisor	The Role is allowed to browse, read live data, read historical data/events, call Methods or subscribe to data/events.
ConfigureAdmin	The Role is allowed to change the non-security related configuration settings.
SecurityAdmin	The Role is allowed to change security related settings.

4.9.3 Evaluating Permissions with Roles

When a Client attempts to access a Node, the Server goes through the list of Roles granted to the Session and logically ORs the Permissions for the Role on the Node. If there are no Node specific Permissions then the default Permissions for the Role in the DefaultRolePermissions Property of the NamespaceMetadata for the namespace the Node belongs to are used (see OPC 10000-5). The resulting mask is the effective Permissions. If the bits corresponding to current operation are set, then the operation can proceed. If they are not set the Server returns Bad_UserAccessDenied.

Roles appear under the Roles Object in the Server Address Space. Each Role has mapping rules defined which appear as Properties of the Role Object (see OPC 10000-5). The examples shown in Table 3 illustrate how the standard mapping rules can be used to determine which Roles a Session has access to and, consequently, the Permissions that are granted to the Session.

Table 3 – Example Roles

Role	Mapping Rules	Description
Anonymous	Identities = Anonymous Applications = Endpoints =	An identity mapping rule that specifies the Role applies to anonymous users.
AuthenticatedUser	Identities = AuthenticatedUser Applications = Endpoints =	An identity mapping rule that specifies the Role applies to authenticated users.
Operator1	Identities = User with name ‘Joe’ Applications = urn:OperatorStation1 Endpoints =	An identity mapping rule that specifies specific users that have access to the Role with a application rule that restricts access to a single Client application.
Operator2	Identities = Users with name ‘Joe’ or ‘Ann’ Applications = urn:OperatorStation2 Endpoints =	An identity mapping rule that specifies specific users that have access to the Role with a application rule that restricts access to a single Client application.
Supervisor	Identities = User with name ‘Root’ Applications = Endpoints =	An identity mapping rule that specifies specific users that have access to the Role
Administrator	Identities = User with name ‘Root’ Applications = Endpoints = opc.tcp://127.0.0.1:48000	An identity mapping rule that specifies specific users that have access to the Role when they connect via a specific Endpoint.

The examples also make use of the Nodes defined in Table 4. The table specifies the value of the RolePermissions Attribute for each Node.

Table 4 – Example Nodes

Node	Role Permissions
Unit1.Measurement	AuthenticatedUser = Browse Operator1 = Browse, Read
Unit2.Measurement	AuthenticatedUser = Browse Operator2 = Browse, Read
SetPoint	AuthenticatedUser = Browse Operator1 and Operator2 = Browse, Read, Write Supervisor = Browse, Read
DisableDevice	AuthenticatedUser = Browse Operator1 and Operator2 = Browse, Read Administrator = Browse, Read, Write

When a Client creates a Session the Roles assigned to the Session depend on the rules defined for each Role. Table 5 lists the assigned Roles for different Sessions created with different Users, Client applications and Endpoints.

Table 5 – Example Role Assignment

User Provided by Client	Roles Assigned to Session
Anonymous	Anonymous
Sam	AuthenticatedUser
Joe using OperatorStation1 application.	AuthenticatedUser, Operator1
Joe using OperatorStation2 application.	AuthenticatedUser, Operator2
Joe using generic application.	AuthenticatedUser
Root using OperatorStation1 application.	AuthenticatedUser, Supervisor
Root using generic application and 127.0.0.1 endpoint.	AuthenticatedUser, Supervisor, Administrator
Root using generic application and another endpoint.	AuthenticatedUser, Supervisor

When a Client application accesses a Node the RolePermissions for the Node are compared to the Roles assigned to the Session. Any Permissions available to at least one Role is granted to the Client. Table 6 provides a number of scenarios and examples and the resulting decision on access.

Table 6 – Examples of Evaluating Access

Use Case	Role Permissions
Anonymous user on localhost browses Unit1.Measurement Node.	Access denied because no rule defined for Anonymous users.
User ‘Sam’ using OperatorStation1 application browses Unit1.Measurement Node.	Allowed because AuthenticatedUser is granted Browse Permission.
User ‘Sam’ using OperatorStation2 application reads Value of Unit1.Measurement Node.	Access denied because AuthenticatedUser is not granted Read Permission.
User ‘Joe’ using OperatorStation1 application reads Value of Unit1.Measurement Node.	Allowed because Operator1 is granted Read Permission.
User ‘Joe’ using OperatorStation2 application reads Value of Unit1.Measurement Node.	Access denied because AuthenticatedUser and Operator2 are not granted Read Permission.
User ‘Joe’ using generic OPC UA application reads Value of Measurement Node.	Access denied because AuthenticatedUser is not granted Read Permission.
User ‘Joe’ using OperatorStation1 application write Value of SetPoint Node.	Allowed because Operator1 is granted Write Permission.
User ‘Root’ using OperatorStation1 application write the Value of SetPoint Node.	Denied because AuthenticatedUser and Supervisor are not granted Write Permission.
User ‘Joe’ using OperatorStation1 application write Value of DisableDevice Node.	Access denied because AuthenticatedUser and Operator1 are not granted Write Permission.
User ‘Root’ using OperatorStation1 application write the Value of DisableDevice Node.	Access denied because AuthenticatedUser and Supervisor are not granted Write Permission.
User ‘Root’ using endpoint 127.0.0.1 to write Value of DisableDevice Node.	Allowed because Administrator is granted Write Permission.