Make the API key for fetching review data available to the build

Note the key is unused.

Refs #19, https://docs.docker.com/build/building/secrets/

.env.dist

@@ -0,0 +1 @@
+PREREVIEW_REVIEWS_DATA_TOKEN=token-here

.github/workflows/ci.yml

@@ -42,6 +42,8 @@ jobs:
           cache-to: type=gha,mode=max,ignore-error=true
           no-cache-filters: build
           target: prod
+          secrets: |
+            PREREVIEW_REVIEWS_DATA_TOKEN=${{ secrets.PREREVIEW_REVIEWS_DATA_TOKEN }}
 
       - name: 'Upload build'
         uses: actions/[email protected]

Dockerfile

@@ -10,7 +10,9 @@ COPY observablehq.config.js observablehq.config.js
 COPY src/ src/
 
 FROM builder AS build
-RUN npx observable build
+RUN --mount=type=secret,id=PREREVIEW_REVIEWS_DATA_TOKEN \
+  PREREVIEW_REVIEWS_DATA_TOKEN=$(cat /run/secrets/PREREVIEW_REVIEWS_DATA_TOKEN) \
+  npx observable build
 
 FROM caddy:2.8.4-alpine AS prod
 COPY Caddyfile /etc/caddy/Caddyfile