mapproxy config that would support internal layer as source

mapproxy.yaml

services:
  demo:
  kml:
  tms:
  wms:
    srs: ['EPSG:4326', 'EPSG:900913']
    image_formats: ['image/jpeg', 'image/png']

layers:
  - name: osm900913
    title: OpenOcean OSM
    sources: [osm_cache_900913]
    
caches:
  osm_cache_900913:
    grids: [global_mercator_osm]
    sources: [osm_tms]
  osm_cache_4326:
    grids: [GLOBAL_GEODETIC]
    sources: [osm_cache_900913]

sources:
  osm_tms:
    type: tile
    url: http://c.tile.openstreetmap.org/%(tms_path)s.png
    grid: global_mercator_osm

grids:
  global_mercator_osm:
    base: GLOBAL_MERCATOR
    origin: nw
    num_levels: 18