_form.html.haml

= form_for(:user) do |f|

  - if flash[:alert]
    %div{class: 'alert'}
      = flash[:alert]

  = f.label :email
  %div{class: 'field'}
    = f.email_field :email

  = f.label :password
  %div{class: 'field'}
    = f.password_field :password

  %div{class: 'actions'}
    = f.submit 'Login'

error.log

PG::UndefinedTable: ERROR: missing FROM-clause entry for table "email" LINE 1: SELECT "users".* FROM "users" WHERE "email"."email" = '' L... ^ : SELECT "users".* FROM "users" WHERE "email"."email" = '' LIMIT 1

ON LINE: user = User.find_by(email: user_param_email).try(:authenticate, user_param_password)

new.html.haml

- title 'Login'

%h1 Login

= render 'form'

routes.rb

Rails.application.routes.draw do
  #match 'login', to: 'sessions#new', as: 'session', via: [:get, :post]
  get 'login', to: 'sessions#new', as: 'session'
  post 'login', to: 'sessions#create', as: 'create_session'
  
  get 'logout', to: 'sessions#destroy', as: 'destroy_session'

  resources :users
end

sessions_controller.rb

class SessionsController < ApplicationController
  def new

  end

  def create
    user = User.find_by(email: params[:email]).try(:authenticate, params[:password])
    if user
      session[:user_id] = user.id
      redirect_to root_url, :notice => 'Logged in!'
    else
      flash.alert = 'Invalid email or password'
      render 'new'
    end
  end

  def destroy
    session[:user_id] = nil
    redirect_to root_url, notice: 'Logged out!'
  end
end