Protected Overrides Function CheckAccessCore(ByVal operationContext As OperationContext) As Boolean
    ' Extract the action URI from the OperationContext. Match this against the claims
    ' in the AuthorizationContext.
    Dim action As String = operationContext.RequestContext.RequestMessage.Headers.Action
    Console.WriteLine("action: {0}", action)

    ' Iterate through the various claim sets in the AuthorizationContext.
    Dim cs As ClaimSet
    For Each cs In operationContext.ServiceSecurityContext.AuthorizationContext.ClaimSets
        ' Examine only those claim sets issued by System.
        If cs.Issuer Is ClaimSet.System Then
            ' Iterate through claims of type "http://example.org/claims/allowedoperation".
            Dim c As Claim
            For Each c In cs.FindClaims("http://example.org/claims/allowedoperation", Rights.PossessProperty)
                ' Write the Claim resource to the console.
                Console.WriteLine("resource: {0}", c.Resource.ToString())

                ' If the Claim resource matches the action URI then return true to allow access.
                If action = c.Resource.ToString() Then
                    Return True
                End If
            Next c
        End If
    Next cs
    ' If we get here, return false, denying access.
    Return False

End Function