public boolean isValidUser(String username) {
		synchronized (repositoryMgr) {
			return userList.containsKey(username);
		}
	}
Returns true if the specified user is known to server.
@param username user name/SID
@return true if user is known to server
Ghidra/Features/GhidraServer/src/main/java/ghidra/server/UserManager.java