What to call the behaviour of the church managers in letting anyone enter depends, perhaps, on what opinion you want to convey about that behaviour.
There is no particular English phrase to describe letting anyone enter, so we can't give you a common idiom.
If you think it's a fool-hardy practice, you might say "The church officials are very lax in not checking whether people have authority to enter the church."
If you agree with the policy, you might say "The church officials have a welcoming and all-inclusive attitude, allowing all and sundry to enter the church."
If you wish to convey no judgement one way or the other, you could say "Anyone is allowed to enter the church."