True, I didn't see they allow to query on ranges. I guess you might be able build something on a BloomFilter Trie for that, but that might be pushing it.

But for one of the calls (checking a whole password against what's stored), which probably accounts for most of the usage of the API, a bloom filter seems like a perfect fit.

Doesn't seem particularly necessary though yeah? Bloom filters are super useful when the cost of doing the computation for the actual lookup is high, but in this case it's a single key-value lookup. That's about as cheap as an operation can possibly get.