Generating Client Secret

Hi,

1. Is it really neccessary to have a private key in order to generate a client secret?

2. Is there a way to generate a client secret without using a private key? How?

3. Based on your documentation (https://developer.apple.com/documentation/signinwithapplerestapi/generate_and_validate_tokens), it mention that the client secret contains header and payload. It didnt mention a private key to generate client secret. We have search some codes on how to generate client secret, and found out that they used private key in order to generate client secret. So how are we going to create a client secret based on your documentation which didnt mention using private key?

Sample header and payload from documentation (https://developer.apple.com/documentation/signinwithapplerestapi/generate_and_validate_tokens)

{
  "alg": "ES256",
  "kid": "ABC123DEFG"
}
{
  "iss": "DEF123GHIJ",
  "iat": 1437179036,
  "exp": 1493298100,
  "aud": "https://appleid.apple.com",
  "sub": "com.mytest.app"
}