code: public static String registerAssertion(String assertion) {
          Map<String, Object> result = parseAssertion(assertion);
          if (result == null)
              return null;
          String email = (String) result.get(ASSERTION_FIELD_EMAIL);
          String origin = (String) result.get(ASSERTION_FIELD_ORIGIN);
          if (origin == null)
              throw new IllegalArgumentException("Invalid assertion, origin was null");
  
          // Normalize the origin URL string:
          try {
              URL originURL = new URL(origin);
              origin = originURL.toExternalForm().toLowerCase();
          } catch (MalformedURLException e) {
              String msg = String.format(Locale.ENGLISH, "Error registering assertion: %s", assertion);
              Log.e(Log.TAG_SYNC, msg, e);
              throw new IllegalArgumentException(msg, e);
          }
  
          List<String> key = new ArrayList<String>();
          key.add(email);
          key.add(origin);
          Log.v(Log.TAG_SYNC, "PersonaAuthorizer registering key: %s", key);
          sAssertions.put(key, assertion);
          return email;
      }
docs: //////////////////////////////////////////////////////////