The Red Dirt Report here describes the process by which the Oklahoma Libertarian Party is deciding whether to let independents vote in the 2018 Libertarian primary. The final decision will be made on October 7.
Back in 2000, the Oklahoma Libertarian Party was also entitled to its own primary, and that year it voted to let all registered voters vote in its primary. However, the State Board of Elections would not permit the party to invite members of other parties to vote in the Libertarian primary. The party sued, and won in the Tenth Circuit. However, then the U.S. Supreme Court reversed the Tenth Circuit, in Clingman v Beaver.