code: public GuacamoleSession getGuacamoleSession(String authToken) 
              throws GuacamoleException {
          
          // Try to get the session from the map of logged in users.
          GuacamoleSession session = tokenSessionMap.get(authToken);
         
          // Authentication failed.
          if (session == null)
              throw new GuacamoleUnauthorizedException("Permission Denied.");
          
          return session;
  
      }
docs: Finds the Guacamole session for a given auth token, if the auth token
  represents a currently logged in user. Throws an unauthorized error
  otherwise.
  
  @param authToken The auth token to check against the map of logged in users.
  @return The session that corresponds to the provided auth token.
  @throws GuacamoleException If the auth token does not correspond to any
  logged in user.