computercraft/auth_server.lua

data = {
    users = {
        ["admin"] = {
            password = "admin"
        }
    }
}

function save_data()
    db = fs.open("auth.db", "w")
    db.write(textutils.serialize(data))
    db.close()
end

function load_data()
    if fs.exists("auth.db") then
        db = fs.open("auth.db", "r")
        db_contents = db.readAll()
        db.close()

        data = textutils.unserialize(db_contents)
    end
end

function generate_token(user)
    local token = textutils.sha256(user .. os.time() .. math.random())
    data.users[user].token = token

    return token
end

function convert_password(password)
    return textutils.sha256(password + "3m&LmNm7")
end

load_data()
math.randomseed(os.time())

while true do
    client_id, msg = rednet.receive()
    request = msg

    if request.action == nil then
        rednet.send(client_id, "invalid request")
    end

    if request.action == "register" then
        if request.username == nil or request.password == nil then
            rednet.send(client_id, "invalid request")
        end

        if data.users[request.username] ~= nil then
            rednet.send(client_id, "user already exists")
        end

        data.users[request.username] = {
            password = convert_password(request.password)
        }

        save_data()

        rednet.send(client_id, "ok")
    end

    if request.action == "login" then
        if request.username == nil or request.password == nil then
            rednet.send(client_id, "invalid request")
        end

        if data.users[request.username] == nil then
            rednet.send(client_id, "user not found")
        end

        if convert_password(request.password) == data.users[request.username].password then
            local token = generate_token(request.username)

            rednet.send(client_id, token)
        else
            rednet.send(client_id, "invalid password")
        end

    end

    if request.action == "token" then
        if request.token == nil then
            rednet.send(client_id, "invalid request")
        end

        for user, userdata in pairs(data.users) do
            if userdata.token == request.token then
                rednet.send(client_id, user)
            end
        end

        rednet.send(client_id, "invalid token")
    end

    if request.action == "profile" then
        if request.username == nil then
            rednet.send(client_id, "invalid request")
        end

        local profile = {}

        if data.users[request.username].profile_data ~= nil then
            profile = data.users[request.username].profile_data
        else
            profile.display_name = request.username
        end

        profile.username = request.username

        rednet.send(client_id, data.users[request.username])
    end

    if request.action == "update_profile" then
        if request.username == nil or request.token == nil then
            rednet.send(client_id, "invalid request")
        end

        if data.users[request.username].token == request.token then
            if request.profile_data ~= nil then
                data.users[request.username].profile_data = request.profile_data
            end

            save_data()

            rednet.send(client_id, "ok")
        else
            rednet.send(client_id, "invalid token")
        end
    end
end