Request an OAuth 2.0 access token

Exchange a Voidnet API key for a short-lived JWT access token using the `client_credentials` grant. The token is valid for a configurable TTL (default 1 hour) and can be used as a `Bearer` credential anywhere an API key is accepted. The `audience` is always the gateway issuer URL — no client-controlled audience is accepted.

curl -X POST "https://example.com/oauth/token" \  -H "Content-Type: application/x-www-form-urlencoded" \  -d 'grant_type=string&client_id=string'

{
  "access_token": "string",
  "expires_in": 0,
  "scope": "string",
  "token_type": "string"
}

{
  "error": "string",
  "error_description": "string"
}

{
  "error": "string",
  "error_description": "string"
}

{
  "error": "string",
  "error_description": "string"
}

{
  "error": "string",
  "error_description": "string"
}