JWT Payload component and security

Sorry if I am not using the right terms. What I meant is the tags that would construct the JWT. Example.

{
"alg": "HS256",
"typ": "JWT"
"sub": "1234567890",
"name": "John Doe",
"admin": true
}

Whats the key-value paid that I need to use and obviously I cant simply type my DF username and password since anyone can decode it. Also, How is the secret key configured in the DF.

Thanks