[Epic] Session Management

[nelsonic]

Context

People expect that "Login" (Authentication / Authorisation) "just works ™".
Nobody wants to have to re-authenticate each time they use a Web App¹.
Being forced to re-authenticate creates usage friction and in some cases abandonment.
When Login fails it can be "catastrophic" to any app, getting it right is worth the investment!

¹The exception to this rule is Online Banking, which has conditioned people to expect a short session duration. This makes perfect sense because financial services are transactional by nature; people login to their Online Banking to perform a specific task like "check balance" or "transfer money" which only takes a few clicks. Very few people have a reason to keep their Online Banking open for longer than a few minutes.
Automatically timing-out a session after 10 minutes of inactivity is the appropriate UX.

Story

As a "user" (person using a web application)
I want to be able to login once and have the App remember me for as long as I'm using the app.
So that I don't have to keep logging in each time I use the App.

We don't want to force people to constantly login to the App because it gets "old" very fast and will result in people being less effective with their time (wasting time logging into apps is a "time tax" nobody wants to keep paying!)

sessions Schema

• inserted_at - (standard ecto/phoenix schema type: :naive_datetime) when a record is inserted. Automatically set by the database which ensures record integrity. This is the start of the session.

• cid (Primary Key. Ecto type :string) - the hash of the data being inserted (the Ecto changeset minus the inserted_at timestamp) such that we know that a record is unique and verifiable.

• session_id - (Ecto type :string) - the hash of the data being inserted (the Ecto changeset minus the inserted_at timestamp) such that we know that a record is unique and verifiable.

• person_id - (Foreign Key: Auth.People.person_id, Ecto type :string) A reference to the person record. Note: as illustrated in the people schema example [Epic] Auth Schema #32 the person_id can refer to an anonomyous (unregistered) person. The same session will continue after they register, this allows for traceability through the analytics/user-journey.

• User Agents Table

  • device_id - the unique identifier of the device including browser user agent and IP Address. this is an irreversible hash which is checked on each request to reduce the chance of session spoofing.

  • ip_address - (Ecto type :binary, Use ) the device IP used for securing the session.

• end - (Ecto type: :naive_datetime) the time when the session ended (usually via "logout" in the case of a registered/logged-in person).

session example

The row² number in the table below corresponds to the action taken.

1. Start - start the session with a particular device. Notice how there is no prev when the session starts.
2. IP Address Change - Whenever a mobile device moves between cell towers its' IP Address can/will change. Some Auth systems will reject subsequent requests from the new IP and force the device to re-authenticate, we need to make this configurable for high-stakes apps (like fintech) , but for now, we are simply going to allow an IP address change provided the session is still valid.
   see: https://android.stackexchange.com/questions/182998/does-ip-address-change-mobile-net
3. End - the session is ended and a timestamp is inserted for the end_at column.

row	inserted_at	cid (PK)	session_id	person_id	ip_address2	end_at	device_id	prev
1	1541609554	2oGsEgN	2oGsEgN	9c	208.67.13.92	null	1BA6546A	null
2	1541609554	e096d100	2oGsEgN	9c	172.34.85.14	null	1BA6546A	2oGsEgN
3	1541609876	ab4362a3	2oGsEgN	9c	172.34.85.14	1541609876	1BA6546A	e096d100

¹Again the row number is included purely for illustrative purposes and would not be needed in the actual table as we already have a cid as Primary Key.

device_id

You may have noticed in the sessions schema above that a session record includes a reference to device_id this is an attempt² to track which device is being used for a particular session so that we can provide a better service.³

We have implemented this Device data "anonymisation" and hashing before in:
https://github.com/dwyl/hits#implementation-detail and https://github.com/dwyl/hits-elixir
So we can easily get the user_agent and ip_address data from the conn

² The reason we say an "attempt" to track which device is making the requests is because we are aware of the fact that both IP Address and Browser User Agent are "spoofable" see: https://en.wikipedia.org/wiki/Spoofing_attack and therefore should not be the only means of trust when a sensitive query is performed.

³ Device list will be stored independently of personal information and used for service quality and analytics exclusively, not to charge iOS/Mac users more, airline/travel industry!!

Todo

We need a sophisticated approach to session management that will ensure
both flawless UX and excellent security for all people using our App on any device.
These are the areas we need to cover:

• Anonymous Sessions - for people who are curious about the App/Site
  but have not yet registered their email address to persist their interactions. ... going to come back to this later!

• Registration with Email address.

• Verification - email address is verified by clicking a link sent by email.

• Re/Set Password - once the person has verified their email address we ask them to define a password so they can login again. This is the same form to be used in the case where the person cannot remember their password and wants to re-set it. (all that changes is the copy)

• Login - the person logs into the App/Site using an email address and password. If either of these two are not present in the people table (or invalid in the case when a password is incorrect), then login will fail with the appropriate (friendly) message. If email and password are valid, show the page they were attempting to reach or their "dashboard".

• Logout - destroy the session on their machine/device and set the end_time in sessions table. Create /logout endpoint #158

Each one of these checklist items will need it's own issue/story with UX/UI flow & logic.
I will get these opened shortly. ⏳

If you are ever in any doubt as to what/how we should implement sessions (or anything else) for Auth, Google is the "reference implementation" to consult.
if you are not already using any Google Apps (G Suite, Gmail, Calendar, Drive, Docs, Meet, etc),
consider trying it out just for professional curiosity.

[nelsonic]

This is the next logical thing to tackle in Auth. After PR #43 is merged. 👍

[nelsonic]

Sessions working as expected:

session.end updated in AuthWeb.AuthController.logout/2 which in turn invokes Auth.Session.end_session/1

[nelsonic]

PR: #159 assigned for review.