# `CCXT.WS.Auth.Expiry`
[🔗](https://github.com/ZenHive/ccxt_client/blob/main/lib/ccxt/ws/auth/expiry.ex#L1)

Pure helpers for computing auth session expiry timing.

Used by the adapter layer (T94/T95) to decide when to schedule an
`:auth_expired` re-auth timer. TTL sources in priority order:

1. **Response-level** — auth response returns `{:ok, %{ttl_ms: N}}` from
   `handle_auth_response/2` (e.g. deribit emits `expires_in` in seconds)
2. **Config-level** — `auth_config[:auth_ttl_ms]` as a static override
3. **None** — no TTL source, no timer scheduled (caller should not re-auth
   on a clock; rely on server-driven auth-failed errors instead)

Not a `CCXT.WS.Auth.Behaviour` implementer — this is a pure utility
shared across patterns that return TTL metadata.

## Example

    auth_meta = %{ttl_ms: 900_000}
    auth_config = %{pattern: :jsonrpc_linebreak}

    ttl_ms = Expiry.compute_ttl_ms(auth_meta, auth_config)
    # => 900_000

    Expiry.schedule_delay_ms(ttl_ms)
    # => 720_000  (80% safety margin)

# `compute_ttl_ms`

```elixir
@spec compute_ttl_ms(map() | nil, map() | nil) :: pos_integer() | nil
```

Resolves the effective TTL (milliseconds) from response metadata and config.

Response-level TTL (`auth_meta.ttl_ms`) wins over config-level
(`auth_config[:auth_ttl_ms]`). Returns `nil` when neither is available.

# `schedule_delay_ms`

```elixir
@spec schedule_delay_ms(pos_integer() | nil) :: pos_integer() | nil
```

Computes the delay before scheduling `:auth_expired`, applying the
80% safety margin and the 24h hard cap.

Returns `nil` for `nil` or non-positive inputs.

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