##前提

macOS mojave 10.14.3
rails 5.1
環境環境 local
Bootstrap、secure_password 導入後

###テーブル

schema.rb

ActiveRecord::Schema.define(version: 20190318144456) do

create_table "users", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8" do |t|
    t.string "name"
    t.string "email"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "image_name"
    t.string "password_digest"
  end

###ルート

routes.rb

Rails.application.routes.draw do
post 'login', to:'users#login'
post 'users/create', to:'users#create'
end

###コントローラー

users_controller.rb


def create
    @user = User.new(
        name: params[:name],
        email: params[:email],
        image_name:"default_user.jpg",
        password: params[:password]
    )
    if @user.save
      session[:user_id] = @user.id
      flash[:notice] = "User registration has been completed."
      @current_user = @user
      redirect_to("/users/#{@user.id}")
    else
      render("users/new")
    end
  end

  def login
    @user = User.find_by(email: params[:email])
    if @user && @user.authenticate(params[:password])
      session[:user_id] = @user.id
      flash[:notice] = "Logged in"
      redirect_to("/posts/index")
    else
      @error_message = "Your email or username is incorrect."
      @email = params[:email]
      @password = params[:password]
      render("users/login_form")
    end
  end

###ユーザー登録フォーム

  <%= form_with url: users_create_path, local: true do |form| %>

new.html.erb

<h1>Sign Up</h1>
  <p>Please fill in this form to create an account.</p>
  <%= form_with url: users_create_path, local: true do |form| %>
    <%= form.label :name %>
    <li>
      <%= form.text_field :name %>
    </li>
    <%= form.label :email %>
    <li>
      <%= form.email_field :email %>
    </li>
    <%= form.label :password %>
    <li>
      <%= form.password_field :password %>
    </li>
    <%= form.label :password_confirmation, "Confirmation" %>
    <li>
      <%= form.password_field :password_confirmation %>
    </li>
    <%= form.submit "Create my account", class: "btn btn-primary" %>
  <% end %>

###ログインフォーム

 <%= form_with url:login_path, local: true do |form| %>

login_form.html.erb

<h1>Log in</h1>
  <p>Please fill in this form to log in.</p>
  <%= form_with url:login_path, local: true do |form| %>
    <%= form.label :name %>
    <li>
      <%= form.text_field :name %>
    </li>
    <%= form.label :email %>
    <li>
      <%= form.email_field :email %>
    </li>
    <%= form.label :password %>
    <li>
      <%= form.password_field :password %>
    </li>
    <%= form.label :password_confirmation, "Confirmation" %>
    <li>
      <%= form.password_field :password_confirmation %>
    </li>
    <%= form.submit "Log in", class: "btn btn-primary" %>
<% end %>

###参考資料
[Rails 5.1] ‘form_with’ APIドキュメント完全翻訳　https://techracho.bpsinc.jp/hachi8833/2017_05_01/39502