Support display method (#86)

* support display service for w3c

* add JSONLDSchemaIden3DisplayMethod constant

verifiable/constants.go

@@ -12,6 +12,9 @@ const (
 	// JSONLDSchemaW3CCredential2018 is a schema for context with VerifiableCredential type
 	JSONLDSchemaW3CCredential2018 = "https://www.w3.org/2018/credentials/v1"
 
+	// JSONLDSchemaW3CCredential2020 is a schema for context with Display method type
+	JSONLDSchemaIden3DisplayMethod = "https://schema.iden3.io/core/jsonld/displayMethod.jsonld"
+
 	// SparseMerkleTreeProof is CredentialStatusType for standard MTP result handlers
 	SparseMerkleTreeProof CredentialStatusType = "SparseMerkleTreeProof"
 
@@ -75,4 +78,7 @@ const (
 
 	// Iden3RefreshService2023 is the type of refresh service
 	Iden3RefreshService2023 RefreshServiceType = "Iden3RefreshService2023"
+
+	// Iden3BasicDisplayMethodV1 is the type fof basic display method
+	Iden3BasicDisplayMethodV1 DisplayMethodType = "Iden3BasicDisplayMethodV1"
 )

verifiable/credential.go

@@ -26,6 +26,7 @@ type W3CCredential struct {
 	CredentialSchema  CredentialSchema       `json:"credentialSchema"`
 	Proof             CredentialProofs       `json:"proof,omitempty"`
 	RefreshService    *RefreshService        `json:"refreshService,omitempty"`
+	DisplayMethod     *DisplayMethod         `json:"displayMethod,omitempty"`
 }
 
 // Merklize merklizes verifiable credential

verifiable/displayMethod.go

@@ -0,0 +1,8 @@
+package verifiable
+
+type DisplayMethodType string
+
+type DisplayMethod struct {
+	ID   string            `json:"id"`
+	Type DisplayMethodType `json:"type"`
+}