UA Part 3: Address Space Model - 4.8.3 Evaluating Permissions with Roles

4.8.3 Evaluating Permissions with Roles

When a Clientattempts to access a Node,the Servergoes through the list of Rolesgranted to the Sessionand logically ORs the Permissionsfor the Roleon the Node. If there are no Node specific Permissions thenthe default Permissionsfor the Rolein the DefaultRolePermissions Property of the NamespaceMetadatafor the namespace the Nodebelongs 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 Serverreturns Bad_UserAccessDenied.

Rolesappear under the Roles Objectin the Server Address Space. Each Rolehas mapping rules defined which appear as Propertiesof the Role Object(see OPC 10000-5). The examples shown in Table 3illustrate how the standard mapping rules can be used to determine which Rolesa Sessionhas access to and, consequently, the Permissionsthat 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 Roleapplies to anonymous users.
AuthenticatedUser	Identities = AuthenticatedUser Applications = Endpoints =	An identity mapping rule that specifies the Roleapplies 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 Rolewith 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 Nodesdefined in Table 4. The table specifies the value of the RolePermissions Attributefor 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 Clientcreates a Sessionthe Rolesassigned to the Sessiondepend on the rules defined for each Role. Table 5lists the assigned Rolesfor different Sessionscreated with different Users, Clientapplications 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 Clientapplication accesses a Nodethe RolePermissionsfor the Nodeare compared to the Rolesassigned to the Session. Any Permissionsavailable to at least one Roleis granted to the Client. Table 6provides 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 Valueof Unit1.Measurement Node.	Access denied because AuthenticatedUser is not granted Read Permission.
User ‘Joe’ using OperatorStation1 application reads Valueof Unit1.Measurement Node.	Allowed because Operator1 is granted Read Permission.
User ‘Joe’ using OperatorStation2 application reads Valueof Unit1.Measurement Node.	Access denied because AuthenticatedUser and Operator2 are not granted Read Permission.
User ‘Joe’ using generic OPC UA application reads Valueof Measurement Node.	Access denied because AuthenticatedUser is not granted Read Permission.
User ‘Joe’ using OperatorStation1 application write Valueof SetPoint Node.	Allowed because Operator1 is granted Write Permission.
User ‘Root’ using OperatorStation1 application write the Valueof 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 Valueof DisableDevice Node.	Access denied because AuthenticatedUser and Supervisor are not granted Write Permission.
User ‘Root’ using endpoint 127.0.0.1 to write Valueof DisableDevice Node.	Allowed because Administrator is granted Write Permission.