Tungsten API defines its own payloads for both inputs and output. The generic structure looks like the following:

{
   "payloadType": "TypeOfPayload",
   "payloadVersion": "1",
   "payload": 
   {
     "key"="value"
   }
}

Where payloadType announces the type of data that will be contained in payload in the given payloadVersion

As an example, a very simple payload is found in the StringPayload data structure and only consists in a key/value pair:

{
   "payloadType": "StringPayload",
   "payloadVersion": "1",
   "payload": 
   {
      "value"="stringvalue"
   }
}

When starting up with a fresh installation of tungsten, if no admin user has been provided to tpm, credentials can be sent to the various functions via the following payload:

{
    "payloadType": "CredentialsPayload",
    "payload":
    {
     "user":"<user>",
     "pass":"<password>"
    }
}

The same payload structure, slightly enriched, will be found in response to listing the user via:

{
    "payloadType": "CredentialsPayload",
    "payloadVersion": "1",
    "payload": {
        "user": "tungsten",
        "pass": "<obfuscated>",
        "access": "full"
    }
}

Various other payloads used and produced by Tungsten REST API entry point will be found in the detailed technical documentation. Links below: