How do I set roles to a User through Global.asax?

Global.asax
 
    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        SetUserRoles()
    End Sub
 
    Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
        SetUserRoles()
    End Sub
 
    Sub SetUserRoles()
        
        If Request.IsAuthenticated Then
            
            
            Using conn As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("db").ConnectionString)
                
                Dim cmd As SqlCommand = New SqlCommand("sp_GetEmployeeAccess", conn)
                Dim reader As SqlDataReader
                
                cmd.CommandType = CommandType.StoredProcedure
                cmd.Parameters.AddWithValue("@Username", User.Identity.Name)
                
                Try
                    
                    conn.Open()
                    reader = cmd.ExecuteReader
                    
                    Dim roleList As New ArrayList
            
                    Do While reader.Read()
                        roleList.Add(reader("AccessID").ToString())
                    Loop
                    
                                
                    Dim roleListArray As String() = roleList.ToArray(GetType(String))
            
                    HttpContext.Current.User = New GenericPrincipal(User.Identity, roleListArray)
                    
                    reader.Close()
                    conn.Close()
                    
                Catch ex As Exception
                    Throw New Exception(ex.Message)
                Finally
                    cmd.Dispose()
                End Try
                
            End Using
        
        End If
        
    End Sub
 
webconfig
 
....
 
  <location path="admin/welcome.aspx">
    <system.web>
      <authorization>
        <allow roles="1"/>
        <deny users="*"/>
      </authorization>      
    </system.web>
  </location>
 
....