Name: registration
Type: request
Purpose: >
  Define ("create") a new participant
Response: registration-confirmation
Inherits: message
Elements:
  Signature: { required: true }
  From: { required: true }
  Date: { required: true }
  Participant-Id: { required: ['Name'], type: identity }
  Name: { required: ['Participant-Id'], type: string, min_length: 3, max_length: 64 }
  Credential: { type: string, min_length: 3, max_length: 96 }
  Consent-Statement: { type: string, max_length: 512 }
  Attributes: { type: object, encryption_required: true }
Notes: >
  The Credential element must contain the SHA256 hash of the original
  credential which will be used for key submission.

  If no Participant-Id is provided, the server will generate one based on the
  provided Name.
Rejection-Codes:
  31: Sender is not authorized to register participants
  41: Missing or differing consent statement
  42: Participant ID has invalid domain
  43: Participant already exists