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

Direct HMAC Expiry auth pattern — bybit, bitmex, and htx/huobi families.

Signs `"GET/realtime{expires}"` with HMAC-SHA256, encodes the signature
as hex (default) or base64, and wraps in an `op: "auth"` frame.

## Example Frame (bybit)

    %{
      "op" => "auth",
      "args" => ["apiKey123", 1699999999999, "signature_hex"]
    }

## Config

| Key | Default | Purpose |
|---|---|---|
| `:expires_offset_ms` | `10_000` | Window added to current `timestamp_ms` |
| `:encoding` | `:hex` | `:hex` or `:base64` signature encoding |
| `:op_field` | `"op"` | Top-level field name (some variants use `"type"`) |
| `:op_value` | `"auth"` | Top-level field value |
| `:timestamp_ms_override` | (unset) | Test-only — freezes the clock |

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