[Trunk | Authorization Library]: AuthorizationService.java: add method "getEmail()", to get user email.

src/main/java/eu/dnetlib/uoaauthorizationlibrary/security/AuthorizationService.java

@@ -76,4 +76,13 @@ public class AuthorizationService {
         }
         return null;
     }
+
+    public String getEmail() {
+        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
+        if (authentication != null && (authentication.getPrincipal() instanceof User)) {
+            User user = (User) authentication.getPrincipal();
+            return user.getUsername();
+        }
+        return null;
+    }
 }