User identities are now strictly URIs for the purposes of authz, messaging, etc. Make the current user URI available via fcrepo-kernel-api. At the very least, change org.fcrepo.kernel.api.FedoraSession#getId() to return this URI.
To capture these URIs in the first place:
- if the provided credentials use a string username, append as a hash to a globally configured baseURI (provide sensible defaults).
- If the provided credentials are a URI, use that.
There may be code in fcrepo4/fcrepo-module-webac that already does this.