List all captive portal Instances

curl --request GET \
  --url https://api.altostrat.io/instances \
  --header 'Authorization: Bearer <token>'

[
  {
    "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "auth_integration_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "strategy": "oauth2",
    "name": "<string>",
    "session_ttl": 123,
    "auth_window_ttl": 123,
    "coupon_ttl": 123,
    "theme": {
      "logo": "<string>",
      "icon": "<string>",
      "accent_text": "<string>",
      "accent_color": "<string>",
      "text_color": "<string>",
      "secondary_text_color": "<string>",
      "background_color": "<string>",
      "border_color": "<string>",
      "box_color": "<string>"
    },
    "terms_text": "<string>",
    "locale": "en",
    "sites": [
      {
        "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
        "subnets": [
          "<string>"
        ]
      }
    ],
    "created_at": "2023-11-07T05:31:56Z",
    "preview_url": "<string>"
  }
]