Brian from Backblaze here. It's pretty simple for now. You can have as many people reading and writing to the same bucket, but they would all need to share the same credentials. Buckets are either "allPublic" or "allPrivate" (and you can flip them back and forth at any time between those two settings). But that's it at this point.
We're actively looking for feedback in this area, so as developers ask us for something like Amazon's IAM (AWS Identity and Access Management) we'll be filling that functionality out. Hopefully without adding too much complexity to the simple model we have now.
Personally I'd like to use some access management, and there's one case that I've not seen solved particularly well (though would appreciate anyone chiming in with things I've missed):
Distinct write and create permissions.
I'd like to be able to grant someone permission to create files but not allow them to modify or delete them later. I end up generally adding this externally.
I think B2 is really close to this, as you've got the file ids for multiple versions, so I can effectively ignore the filenames and use the file ids instead. It'd need a difference between "upload new version" and "delete version" though.
We're actively looking for feedback in this area, so as developers ask us for something like Amazon's IAM (AWS Identity and Access Management) we'll be filling that functionality out. Hopefully without adding too much complexity to the simple model we have now.