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# lib/phoenix_admin/accounts/current_user.ex
defmodule PhoenixAdmin.Accounts.CurrentUser do
  import Plug.Conn
  import Guardian.Plug

  def init(opts), do: opts

  def call(conn, _opts) do
    current_user = current_resource(conn)
    assign(conn, :current_user, current_user)

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# lib/phoenix_admin_web/views/session_view.ex
defmodule PhoenixAdminWeb.SessionView do
  use PhoenixAdminWeb, :view
end

# lib/phoenix_admin_web/template/new.html.eex
<%= form_for @changeset, Routes.session_path(@conn, :login), fn f -> %>
  <%= if @changeset.action do %>
    <div class="alert alert-danger">
      <p>Oops, something went wrong! Please check the errors below.</p>

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defmodule PhoenixAdminWeb.SessionController do
  use PhoenixAdminWeb, :controller

  alias PhoenixAdmin.Accounts
  alias PhoenixAdmin.Accounts.User

  def new(conn, _) do
    changeset = Accounts.change_user(%User{})

    conn

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# lib/phoenix_admin/accounts/user.ex
defmodule PhoenixAdmin.Accounts.User do
  use Ecto.Schema
  import Ecto.Changeset
  alias Argon2

  schema "users" do
    field :email, :string
    field :name, :string
    field :password, :string

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# lib/phoenix_admin/accounts/pipeline.ex
defmodule PhoenixAdmin.Accounts.Pipeline do
  use Guardian.Plug.Pipeline,
    otp_app: :phoenix_admin,
    module: PhoenixAdmin.Accounts.Guardian,
    error_handler: PhoenixAdmin.Accounts.ErrorHandler

  # セッショントークンの場合の検証
  plug Guardian.Plug.VerifySession
  # 認証ヘッダーの場合の検証

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# lib/phoenix_admin_web/controllers/user_controller.ex

  alias PhoenixAdmin.Accounts
  alias PhoenixAdmin.Accounts.User
  # alias PhoenixAdmin.{Accounts, Accounts.User, ..} とまとめて書ける

  def create(conn, %{"user" => user_params}) do
    case Accounts.create_user(user_params) do
      {:ok, user} ->
        conn

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  def authenticate_user(email, plain_text_password) do
    query = from u in User, where: u.email == ^email
    case Repo.one(query) do
      nil ->
        Argon2.no_user_verify()
        {:error, :invalid_credentials}
      user ->
        if Argon2.verify_pass(plain_text_password, user.password) do
          {:ok, user}
        else

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# lib/phoenix_admin/accounts/error_handler.ex
defmodule PhoenixAdmin.Accounts.ErrorHandler do
  import Plug.Conn

  @behaviour Guardian.Plug.ErrorHandler

  @impl Guardian.Plug.ErrorHandler
  def auth_error(conn, {type, _reason}, _opts) do
    body = to_string(type)
    conn

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# lib/phoenix_admin/accounts/guardian.ex
defmodule PhoenixAdmin.Accounts.Guardian do
  use Guardian, otp_app: :phoenix_admin

  alias PhoenixAdmin.Accounts

  def subject_for_token(resource, _claims) do
    sub = to_string(resource.id)
    {:ok, sub}
  end