# `Gamend.Accounts.UserToken`
[🔗](https://github.com/appsinacup/gamend/blob/v1.0.7/lib/gamend/accounts/user_token.ex#L1)

Functions and schema for persistent user tokens used by sessions, magic links,
and email-change workflows.

Tokens generated by this module are stored hashed when sent via email and
stored raw for session tokens (which are signed). The module provides helper
queries for verification and convenient builders used throughout the app.

# `t`

```elixir
@type t() :: %Gamend.Accounts.UserToken{
  __meta__: term(),
  authenticated_at: DateTime.t() | nil,
  context: String.t() | nil,
  id: Ecto.UUID.t() | nil,
  inserted_at: DateTime.t() | nil,
  sent_to: String.t() | nil,
  token: binary() | nil,
  user: Gamend.Accounts.User.t() | Ecto.Association.NotLoaded.t() | nil,
  user_id: Ecto.UUID.t() | nil
}
```

# `build_email_token`

Builds a token and its hash to be delivered to the user's email.

The non-hashed token is sent to the user email while the
hashed part is stored in the database. The original token cannot be reconstructed,
which means anyone with read-only access to the database cannot directly use
the token in the application to gain access. Furthermore, if the user changes
their email in the system, the tokens sent to the previous email are no longer
valid.

Users can easily adapt the existing code to provide other types of delivery methods,
for example, by phone numbers.

# `build_session_token`

Generates a token that will be stored in a signed place,
such as session or cookie. As they are signed, those
tokens do not need to be hashed.

The reason why we store session tokens in the database, even
though Phoenix already provides a session cookie, is because
Phoenix' default session cookies are not persisted, they are
simply signed and potentially encrypted. This means they are
valid indefinitely, unless you change the signing/encryption
salt.

Therefore, storing them allows individual user
sessions to be expired. The token system can also be extended
to store additional data, such as the device used for logging in.
You could then use this information to display all valid sessions
and devices in the UI and allow users to explicitly expire any
session they deem invalid.

# `expired_query`

```elixir
@spec expired_query() :: Ecto.Query.t()
```

Query selecting token rows that are past their own context's validity window.

Each context expires on a different clock (session 14d, magic link 15min,
email change 7d), and those windows live here — so retention inverts the
same predicate the verify queries use instead of guessing a single age.
Contexts this module does not know are never selected.

# `verify_change_email_token_query`

Checks if the token is valid and returns its underlying lookup query.

The query returns the user_token found by the token, if any.

This is used to validate requests to change the user
email.
The given token is valid if it matches its hashed counterpart in the
database and if it has not expired (after @change_email_validity_in_days).
The context must always start with "change:".

# `verify_magic_link_token_query`

Checks if the token is valid and returns its underlying lookup query.

If found, the query returns a tuple of the form `{user, token}`.

The given token is valid if it matches its hashed counterpart in the
database. This function also checks if the token is being used within
15 minutes. The context of a magic link token is always "login".

# `verify_session_token_query`

Checks if the token is valid and returns its underlying lookup query.

The query returns the user found by the token, if any, along with the token's creation time.

The token is valid if it matches the value in the database and it has
not expired (after @session_validity_in_days).

---

*Consult [api-reference.md](api-reference.md) for complete listing*