When external subservers register themselves to be served through the
same gRPC interface as the main lnd RPC, their requests are also
intercepted by the main lnd macaroon interceptor.
If the external subservers want to use their own macaroons that are
independent of lnd's, they need a way to overwrite the default validator
of the macaroon interceptor. We add this mechanism with the concept of
external validators.
To make the permission system even more fine-grained, we want to allow
users to specify exact gRPC URIs in the macaroon permissions instead of
just broad entity/action groups.
For this we add the special entity "uri" which allows an URI specific
permission to be defined as "uri:/lnrpc.Lightning/GetInfo" for example
instead of the more coarse "info:read" which gives access to multiple
URIs.
This commit is a step to split the lnwallet package. It puts the Input
interface and implementations in a separate package along with all their
dependencies from lnwallet.
This commit reworks the macaroon authentication framework to use the
v2 macaroon format and bakery API. It also replaces the code in each
RPC method which calls the macaroon verifier with interceptors which
call the macaroon verifier instead. In addition, the operation
permissions are reworked to fit the new format of "allow" commands
(specifically, entity/operation permissions instead of method
permissions).
This commit is a precautionary commit put in place in order to ensure
that the logic of macaroon retrieval doesn’t run into a bug triggered
by returning a reference into bolt’s active memory map. This can arise
if one returns a pointer directly read from the database. We seek to
avoid this by instead ensuring all byte slices are fully copied before
returning.
