CredentialRequestMessage
@contextstring[]required
Example: 
["https://w3id.org/dspace-dcp/v1.0/dcp.jsonld"]typestringrequired
Example: 
CredentialRequestMessageholderPidstringrequired
credentials object[]required
Array [
idstringrequired
]
CredentialRequestMessage
{
  "@context": [
    "https://w3id.org/dspace-dcp/v1.0/dcp.jsonld"
  ],
  "type": "CredentialRequestMessage",
  "holderPid": "string",
  "credentials": [
    {
      "id": "string"
    }
  ]
}