{
  "status": "challenge",
  "instructions": "Echo compute HMAC-SHA256(challengeToken, sharedSecret) as X-Challenge-Response",
  "headers": {
    "X-Challenge-Token": "rI0_lfU_L71JCKXF02GvY-Gil9g7KtdgKrfLp9WeF68",
    "X-Challenge-Response": "[HMAC_RESULT]"
  },
  "example": {
    "curl": "curl -X POST https://living-documentation.prod.cmi.ch/api/auth/challenge -H 'X-Challenge-Token: rI0_lfU_L71JCKXF02GvY-Gil9g7KtdgKrfLp9WeF68' -H 'X-Challenge-Response: [HMAC]'"
  }
}