## Create an ephemeral Viewer session

**post** `/v1/viewer/ephemeral-sessions`

Mints a 30-second tokenized landing URL for a userless, studyless Viewer session. The token names a customer retrievalId (not an Avara study). Optional options are echoed verbatim on ephemeral.access_requested (max 3072 bytes JSON). Optional hangingProtocol applies a single-monitor layout when the viewer loads. Requires a customer study webhook on the API key.

### Body Parameters

- `retrievalId: string`

  Opaque customer handle for this view session. Avara stores and echoes it; it is not an Avara study ID.

- `hangingProtocol: optional EphemeralHangingProtocol`

  Optional single-monitor hanging protocol applied when the ephemeral viewer loads. Omitted = no protocol. Invalid shape is rejected.

  - `layout: ViewerLayout`

    Viewport grid layout for an ephemeral hanging protocol. Wire values match first-party viewer layouts ('1x1' through '4x4').

    - `"1x1"`

    - `"1x2"`

    - `"1x3"`

    - `"1x4"`

    - `"2x1"`

    - `"2x2"`

    - `"2x3"`

    - `"2x4"`

    - `"3x1"`

    - `"3x2"`

    - `"3x3"`

    - `"3x4"`

    - `"4x1"`

    - `"4x2"`

    - `"4x3"`

    - `"4x4"`

  - `viewportAssignments: array of string`

- `options: optional map[unknown]`

  Optional JSON object echoed verbatim on ephemeral.access_requested. Avara does not read or edit it. Hard cap 3072 bytes on JSON.stringify. Examples: studyInstanceUids or internal ids for multi-study reads. Not for URLs or manifests.

### Returns

- `url: string`

### Example

```http
curl https://api.avarasoftware.com/v1/viewer/ephemeral-sessions \
    -H 'Content-Type: application/json' \
    -H "Authorization: Bearer $AVARA_API_KEY" \
    -d '{
          "retrievalId": "order-12345",
          "hangingProtocol": {
            "layout": "2x2",
            "viewportAssignments": [
              "Axial T1",
              "Axial T2",
              null,
              "Sagittal T2"
            ]
          }
        }'
```

#### Response

```json
{
  "url": "https://viewer.avarasoftware.com/token/landing?token=abc123"
}
```