Invalidate existing sessions when changing email or password

As we don't have any way to actually find the active sessions for
an account we instead store a fingerprint in the session, and refuse
to use any session with a different fingerprint.

app/controllers/application_controller.rb

@@ -23,7 +23,11 @@ class ApplicationController < ActionController::Base
     if session[:user]
       self.current_user = User.where(:id => session[:user]).where("status IN ('active', 'confirmed', 'suspended')").first
 
-      if current_user.status == "suspended"
+      if session[:fingerprint] &&
+         session[:fingerprint] != current_user.fingerprint
+        reset_session
+        self.current_user = nil
+      elsif current_user.status == "suspended"
         session.delete(:user)
         session_expires_automatically
 
@@ -42,6 +46,8 @@ class ApplicationController < ActionController::Base
     elsif session[:token]
       session[:user] = current_user.id if self.current_user = User.authenticate(:token => session[:token])
     end
+
+    session[:fingerprint] = current_user.fingerprint if current_user && session[:fingerprint].nil?
   rescue StandardError => e
     logger.info("Exception authorizing user: #{e}")
     reset_session

app/controllers/users_controller.rb

@@ -183,6 +183,7 @@ class UsersController < ApplicationController
 
           if current_user.save
             token.destroy
+            session[:fingerprint] = current_user.fingerprint
             flash[:notice] = t "users.reset_password.flash changed"
             successful_login(current_user)
           end
@@ -323,6 +324,7 @@ class UsersController < ApplicationController
           token.destroy
 
           session[:user] = user.id
+          session[:fingerprint] = user.fingerprint
 
           redirect_to referer || welcome_path
         end
@@ -368,6 +370,7 @@ class UsersController < ApplicationController
         end
         current_user.tokens.delete_all
         session[:user] = current_user.id
+        session[:fingerprint] = current_user.fingerprint
         redirect_to :action => "account", :display_name => current_user.display_name
       elsif token
         flash[:error] = t "users.confirm_email.failure"
@@ -552,6 +555,7 @@ class UsersController < ApplicationController
   # process a successful login
   def successful_login(user, referer = nil)
     session[:user] = user.id
+    session[:fingerprint] = user.fingerprint
     session_expires_after 28.days if session[:remember_me]
 
     target = referer || session[:referer] || url_for(:controller => :site, :action => :index)
@@ -642,6 +646,8 @@ class UsersController < ApplicationController
     end
 
     if user.save
+      session[:fingerprint] = user.fingerprint
+
       set_locale(true)
 
       if user.new_email.blank? || user.new_email == user.email

app/models/user.rb

@@ -44,6 +44,7 @@
 #
 
 class User < ApplicationRecord
+  require "digest"
   require "xml/libxml"
 
   has_many :traces, -> { where(:visible => true) }
@@ -306,6 +307,13 @@ class User < ApplicationRecord
     ClientApplication.find_by(:key => application_key).access_token_for_user(self)
   end
 
+  def fingerprint
+    digest = Digest::SHA256.new
+    digest.update(email)
+    digest.update(pass_crypt)
+    digest.hexdigest
+  end
+
   private
 
   def set_defaults