How would YOU write a script for a lightswitch to only toggle when authorised people do it?

LocalScript Way You can declare a boolean variable called isAuthorized and change it in one of your custom function, and then use a conditional statement that checks if the player is authorized to use the lightswitch, something like this:

local player = game.Players.LocalPlayer
local isAuthorized = false
function togglePlayerAuth()
    if not isAuthorized then
        isAuthorized = true
    else
        isAuthorized = false
    end
end

game.Workspace.YourLightswitch.MouseClick:connect(function(p)
    if not isAuthorized then
        -- Your code
    else
        -- Your code
    end
end)

Script Way You can declare a BoolValue called "isAuthorized" this too, same way of the LocalScript way.

function onPlayerLogin(p)
    local tempdata = p:FindFirstChild("TempData")
    if not tempdata then
        tempdata = Instance.new("Model", p)
        tempdata.Name = "TempData"
    else
        local isAuthorized = tempdata:FindFirstChild("IsAuthorized")
        if not isAuthorized then
            isAuthorized = Instance.new("BoolValue", tempdata)
            isAuthorized.Name = "IsAuthorized"
            isAuthorized.Value = false
        end
    end
end

function togglePlayerAuth(player)
    player:WaitForChild("TempData")
    local tempdata = player:FindFirstChild("TempData")
    local isAuthorized = player:FindFirstChild("IsAuthorized")
    if isAuthorized.Value == false then
        isAuthorized.Value = true
    else
        isAuthorized.Value = false
    end
end

game.Workspace.YourLightswitch.MouseClick:connect(function(p)
    local tempdata = p:FindFirstChild("TempData")
    local isAuthorized = tempdata:FindFirstChild("IsAuthorized")
    if isAuthorized.Value == false then
        -- Your code
    else
        -- Your code
    end
end

game.Players.PlayerAdded:connect(onPlayerLogin)

WARNING: Be aware when selecting from LocalScript or Script, if you use LocalScript then the code will execute on the CURRENT PLAYER RUNNING THE SCRIPT; If you instead of the LocalScript you decide to use the Script (the normal one) then this code will run on EACH PLAYER CALLED FROM THE FUNCTION!