fix(protocol): user entity id not encoded correctly (#98)

This fixes an issue where the protocol.UserEntity field ID was encoded with Base64 URL Encoding with padding instead of without padding.

Fixes #97

protocol/attestation_test.go

@@ -91,7 +91,7 @@ var testAttestationOptions = []string{
 		"user": {
 			"name": "self",
 			"displayName": "self",
-			"id": "2iEAAAAAAAAAAA=="
+			"id": "2iEAAAAAAAAAAA"
 		},
 		"pubKeyCredParams": [
 			{
@@ -116,7 +116,7 @@ var testAttestationOptions = []string{
 		"user": {
 			"name": "flort",
 			"displayName": "flort",
-			"id": "1DMAAAAAAAAAAA=="
+			"id": "1DMAAAAAAAAAAA"
 		},
 		"pubKeyCredParams": [
 			{
@@ -142,7 +142,7 @@ var testAttestationOptions = []string{
 		  "user": {
 			"name": "testuser1",
 			"displayName": "testuser1",
-			"id": "1zMAAAAAAAAAAA=="
+			"id": "1zMAAAAAAAAAAA"
 		  },
 		  "pubKeyCredParams": [
 			{

protocol/entities.go

@@ -44,5 +44,5 @@ type UserEntity struct {
 	// authentication and authorization decisions MUST be made on the basis of this id
 	// member, not the displayName nor name members. See Section 6.1 of
 	// [RFC8266](https://www.w3.org/TR/webauthn/#biblio-rfc8266).
-	ID []byte `json:"id"`
+	ID URLEncodedBase64 `json:"id"`
 }