https://tools.ietf.org/html/rfc8040#section-1.3

The server MUST implement the "ietf-yang-library" module, which MUST identify all of the YANG modules used by the server, in the "modules-state/module" list

The following query contains modules-state/module list:

curl -u admin:admin http://localhost:8181/rests/data

However the following queries fail:

curl -u admin:admin http://localhost:8181/rests/data/ietf-yang-library:modules-state

curl -u admin:admin http://localhost:8181/rests/data/ietf-yang-library:modules-state/module=ietf-yang-library,2019-01-04