support refresh service (#81)

* support refresh service
* add custom type for refresh service

---------

Co-authored-by: vmidyllic <74898029+vmidyllic@users.noreply.github.com>

Author: ilya-korotya

verifiable/constants.go

@@ -72,4 +72,7 @@ const (
 
 	// Iden3OnсhainSparseMerkleTreeProof2023 is a proof type for MTP proofs with iden3 metadata from blockchain
 	Iden3OnchainSparseMerkleTreeProof2023 CredentialStatusType = "Iden3OnchainSparseMerkleTreeProof2023"
+
+	// Iden3RefreshService2023 is the type of refresh service
+	Iden3RefreshService2023 RefreshServiceType = "Iden3RefreshService2023"
 )

verifiable/credential.go

@@ -25,6 +25,7 @@ type W3CCredential struct {
 	Issuer            string                 `json:"issuer"`
 	CredentialSchema  CredentialSchema       `json:"credentialSchema"`
 	Proof             CredentialProofs       `json:"proof,omitempty"`
+	RefreshService    *RefreshService        `json:"refreshService,omitempty"`
 }
 
 // Merklize merklizes verifiable credential

verifiable/refreshService.go

@@ -0,0 +1,10 @@
+package verifiable
+
+// RefreshServiceType represent refresh service types
+type RefreshServiceType string
+
+// RefreshService is struct that represents refresh service json-ld document
+type RefreshService struct {
+	ID   string             `json:"id"`
+	Type RefreshServiceType `json:"type"`
+}