Normal UPDATE: This is happening with all tech using '/api/' in the URL, not only Docker.
Attached plugin script is being used to detect request headers.
The ubuntu:latest image is being copied to 'docker-local' to compare the results.
For 'docker-local', the plugin detects request headers.
$ curl -vvv -H "X-JFrog-Art-Api:AKCp5bu9HHBiktERAiG8dNfBPXJVhBr5Yoj6jA3EAabmrqBEiw7nZ66MTfG7hFfxV45Tvyto9" http://localhost:8081/artifactory/api/docker/docker-local/v2/ubuntu/blobs/sha256:84ed7d2f608f8a65d944b40132a0333069302d24e9e51a6d6b338888e8fd0a6b -O
2019-01-08 16:25:39,626 [http-nio-8081-exec-15] [INFO ] (o.j.r.d.v.r.h.DockerV2LocalRepoHandler:117) - Fetching docker blob 'sha256:84ed7d2f608f8a65d944b40132a0333069302d24e9e51a6d6b338888e8fd0a6b' from repo 'docker-local' 2019-01-08 16:25:39,641 [http-nio-8081-exec-15] [WARN ] (docker-test :21) - BeforeDownload: Headers exist 2019-01-08 16:25:39,648 [http-nio-8081-exec-15] [WARN ] (docker-test :10) - AltResponse: Headers exist
For 'docker-remote', the plugin doesn't detect request headers and always returns 404 code.
$ curl -vvv -H "X-JFrog-Art-Api:AKCp5bu9HHBiktERAiG8dNfBPXJVhBr5Yoj6jA3EAabmrqBEiw7nZ66MTfG7hFfxV45Tvyto9" http://localhost:8081/artifactory/api/docker/docker-remote/v2/ubuntu/blobs/sha256:84ed7d2f608f8a65d944b40132a0333069302d24e9e51a6d6b338888e8fd0a6b -O
2019-01-08 16:25:19,012 [http-nio-8081-exec-8] [INFO ] (o.a.a.d.r.v.DockerV2RemoteRepoHandler:172) - Fetching docker blob 'sha256:84ed7d2f608f8a65d944b40132a0333069302d24e9e51a6d6b338888e8fd0a6b'
2019-01-08 16:25:19,601 [http-nio-8081-exec-8] [WARN ] (docker-test :23) - BeforeDownload: Request has no headers
2019-01-08 16:25:19,688 [http-nio-8081-exec-8] [WARN ] (docker-test :12) - AltResponse: Request has no headers