Use sorcery for logins

This gives us more flexibility and allows us to use password authentication
later. Also we don't need to build the login functionality ourself.

db/migrate/20200413101920_sorcery_core.rb

@@ -0,0 +1,15 @@
+class SorceryCore < ActiveRecord::Migration[6.0]
+  def change
+    add_column :users, :crypted_password, :string
+    add_column :users, :salt, :string
+    add_column :users, :magic_login_token, :string
+    add_column :users, :magic_login_token_expires_at, :datetime
+    add_column :users, :magic_login_email_sent_at, :datetime
+
+    add_column :authentications, :provider, :string, null: false
+    add_column :authentications, :uid, :string, null: false
+
+    add_index :users, :magic_login_token
+    add_index :users, :email, unique: true
+  end
+end