Why doesn't GeoServer WMTS work with SQL View parameters

Question

[QUESTION] Why doesn't GeoServer WMTS work with SQL View parameters?

My Setup

I'm using GeoServer 2.26 with a SQL View layer that works correctly with WFS and WMS, but fails with WMTS. Here's my configuration:

SQL View Definition:

SELECT 
 map_uuid AS "mapUuid", 
 geom, 
 geom_id AS "geometryId", 
 zone, 
 round(value, 2) AS "value",
 created_date AS "createdDate", 
 round(ST_Area(geom, true)::numeric, 2) AS "sqm"
FROM public.equation_pixel_map 
WHERE map_uuid = '%mapUuid%'

with defined SQL view parameters mapUuid (default value and validation regular expression)

The Problem

When I make a WMTS request with parameters, I get empty results:

http://localhost:8080/gwc/service/wmts?REQUEST=GetTile&SERVICE=WMTS&VERSION=1.0.0&LAYER=agri:equation_pixel_map_view&STYLE=&TILEMATRIX=EPSG:4326:0&TILEMATRIXSET=EPSG:4326&FORMAT=application/json;type=geojson&TILECOL=1&TILEROW=0&VIEWPARAMS=UUID:ee763f5a-ef5d-4119-827d-c67aa0fc6fb6

What Works

• WMTS requests without parameters to original table returns non-empty results:

http://localhost:8080/gwc/service/wmts?REQUEST=GetTile&SERVICE=WMTS&VERSION=1.0.0&LAYER=agri:equation_pixel_map&STYLE=&TILEMATRIX=EPSG:4326:0&TILEMATRIXSET=EPSG:4326&FORMAT=application/json;type=geojson&TILECOL=1&TILEROW=0

• WFS requests with the same parameter work fine:

http://localhost:8080/agri/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=agri:equation_pixel_map_view&VIEWPARAMS=mapUuid:072db89a-a031-4ab4-b173-2c59115550b0

• WMS requests also work correctly:

http://localhost:8080/agri/wms?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=application/json;type=geojson&LAYERS=agri:equation_pixel_map_view&STYLES=&CRS=EPSG:4326&BBOX=-180,-90,180,90&WIDTH=1024&HEIGHT=512&VIEWPARAMS=mapUuid:072db89a-a031-4ab4-b173-2c59115550b0

Questions

1. Why doesn't WMTS respect the VIEWPARAMS like WMS and WFS do?
2. Do I need special configuration for WMTS to work with parameterized SQL Views?
3. Is there a way to set up GeoWebCache to properly handle SQL View parameters?
4. Are there any known limitations with WMTS and parameterized views?

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Answer 1

I didn't think there was any mechanism in GeoWebCache to pass ViewParams (or other unexpected keywords) to GeoServer. However, this issue suggests that it is possible in KVP mode, see also this for details of the filter procedure.