code: public String getContainerAuthDataID() {
          String authDataID = null;
          lock.readLock().lock();
          try {
              if (containerAuthDataRef != null) {
                  authDataID = (String) containerAuthDataRef.getProperty(ID);
                  if (authDataID == null ||
                      DEFAULT_PATTERN.matcher(authDataID).matches() ||
                      DEFAULT_NESTED_PATTERN.matcher(authDataID).matches()) {
                      authDataID = (String) containerAuthDataRef.getProperty("config.displayId");
                  }
              }
          } finally {
              lock.readLock().unlock();
          }
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
              Tr.debug(this, tc, "default container auth data", authDataID);
          return authDataID;
      }
docs: Returns the id of the authData element for the default container managed auth alias (if any).
  
  @return the id of the authData element for the default container managed auth alias (if any).