PKCE における S256 指定の強制化

% curl -s -X POST .../auth/authorization
  -H "Authorization: Bearer <Service Access Token e.g., Xg6jVpJCvsaXvy2ks8R5WzjdMYlvQqOym3slDX0wNhQ>' \
  -H 'Content-Type: application/json' \
  -d '{ "parameters": "redirect_uri=...
    &response_type=code
    &client_id=...
    &scope=...
    &code_challenge=...
    &code_challenge_method=plain" }'

{
  "resultCode": "A124308",
  "resultMessage": "[A124308] The value of the 'code_challenge_method' request parameter must be 'S256'.",
  ...
}