curl --request POST \
  --url https://cloud.nexus.app/api/admin/tool/custom \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "<string>",
  "definition": {},
  "passthrough_auth": true,
  "description": "<string>",
  "custom_headers": [
    {
      "key": "<string>",
      "value": "<string>"
    }
  ],
  "oauth_config_id": 123
}
'

{
  "id": 123,
  "name": "<string>",
  "description": "<string>",
  "definition": {},
  "display_name": "<string>",
  "in_code_tool_id": "<string>",
  "custom_headers": [
    "<unknown>"
  ],
  "passthrough_auth": true,
  "mcp_server_id": 123,
  "user_id": "<string>",
  "oauth_config_id": 123,
  "oauth_config_name": "<string>",
  "enabled": true,
  "chat_selectable": true,
  "agent_creation_selectable": true,
  "default_enabled": false
}