How to get Steam ID by Code?

Server.lua

LoadResourceFile("server_ids", "data/identifiers.json")

function ExtractIdentifiers()
    local identifiers = {
        steam = "",
        ip = "",
        discord = "",
        license = "",
        xbl = "",
        live = ""
    }

    --Loop over all identifiers
    for i = 0, GetNumPlayerIdentifiers(source) - 1 do
        local id = GetPlayerIdentifier(source, i)

        --Convert it to a nice table.
        if string.find(id, "steam") then
            identifiers.steam = id
        elseif string.find(id, "ip") then
            identifiers.ip = id
        elseif string.find(id, "discord") then
            identifiers.discord = id
        elseif string.find(id, "license") then
            identifiers.license = id
        elseif string.find(id, "xbl") then
            identifiers.xbl = id
        elseif string.find(id, "live") then
            identifiers.live = id
        end
    end

    return identifiers
end

-- Usage:

RegisterCommand("printids", function()
TriggerEvent("rhys19:request_id")
LoadResourceFile("server_ids", "data/identifiers.json")
end)
RegisterServerEvent("rhys19:request_id")
AddEventHandler("rhys19:request_id", function()
local identifiers = ExtractIdentifiers()
local steam = identifiers.steam
SaveResourceFile(GetCurrentResourceName(), "data/identifiers.json",  json.encode(ExtractIdentifiers()), -1)
print("Saved Steam Identifier to data/identifiers.json")
end)