Merge branch 'master' into validation

src/main/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactory.java

@@ -67,6 +67,13 @@ public class IdentifierFactory implements Serializable {
 		DELEGATED_PID_AUTHORITY.get(PidType.doi).put(ZENODO_R3_ID, "zenodo");
 	}
 
+	public static Set<String> delegatedAuthorityDatasourceIds() {
+		return DELEGATED_PID_AUTHORITY.values()
+				.stream()
+				.flatMap(m -> m.keySet().stream())
+				.collect(Collectors.toCollection(HashSet::new));
+	}
+
 	public static List<StructuredProperty> getPids(List<StructuredProperty> pid, KeyValue collectedFrom) {
 		return pidFromInstance(pid, collectedFrom, true).distinct().collect(Collectors.toList());
 	}