code: public static String getUser() {
          String accessid = null;
          WSCredential credential = getCallerWSCredential();
  
          try {
              if (credential != null && !credential.isUnauthenticated())
                  accessid = credential.getAccessId();
          } catch (Exception e) {
              if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                  Tr.debug(tc, "Internal error: " + e);
          }
          return accessid;
      }
docs: Return the accessid of the current subject on the thread
  
  @return the access id, or null if there is no subject or no WSCredential