SpiceDB is an open source, Google Zanzibar-inspired, database system for creating and managing security-critical application permissions.

SpiceDB

Also 

I had a doubt about caching of wildcards 

Is a wildcard cached in the context of both subject and resource

Or

Or is it cached just in the context of resource only?

eg

definition folder {
  Relation: admin:user:*
}

Will the the cache have (as keys) just folder,

Or it will have the context of both user along with  folder?

the things that get cached are the subproblems that make up a permission computation

so the answer to this specific question is "it depends"