diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 1b41278a7f..dcf7d78f1d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,6 +21,7 @@ concurrency:
 jobs:
   ci-config:
     name: config
+    if: vars.CI_BRANCHES == '' || contains(vars.CI_BRANCHES, github.ref_name)
     runs-on: ubuntu-latest
     outputs:
       enabled: ${{ steps.check-ref.outputs.enabled }}${{ steps.skip-if-redundant.outputs.enabled }}
@@ -43,10 +44,13 @@ jobs:
         name: check whether CI is enabled for ref
         run: |
           enabled=yes
-          if test -x config-repo/ci/config/allow-ref &&
-             ! config-repo/ci/config/allow-ref '${{ github.ref }}'
+          if test -x config-repo/ci/config/allow-ref
           then
-            enabled=no
+            echo "::warning::ci/config/allow-ref is deprecated; use CI_BRANCHES instead"
+            if ! config-repo/ci/config/allow-ref '${{ github.ref }}'
+            then
+              enabled=no
+            fi
           fi
 
           skip_concurrent=yes
diff --git a/ci/config/README b/ci/config/README
new file mode 100644
index 0000000000..8de3a04e32
--- /dev/null
+++ b/ci/config/README
@@ -0,0 +1,14 @@
+You can configure some aspects of the GitHub Actions-based CI on a
+per-repository basis by setting "variables" and "secrets" from with the
+GitHub web interface. These can be found at:
+
+  https://github.com/<user>/git/settings/secrets/actions
+
+The following variables can be used:
+
+ - CI_BRANCHES
+
+   By default, CI is run when any branch is pushed. If this variable is
+   non-empty, then only the branches it lists will run CI. Branch names
+   should be separated by spaces, and should use their shortened form
+   (e.g., "main", not "refs/heads/main").
diff --git a/ci/config/allow-ref.sample b/ci/config/allow-ref.sample
deleted file mode 100755
index af0e076f8a..0000000000
--- a/ci/config/allow-ref.sample
+++ /dev/null
@@ -1,27 +0,0 @@
-#!/bin/sh
-#
-# Sample script for enabling/disabling GitHub Actions CI runs on
-# particular refs. By default, CI is run for all branches pushed to
-# GitHub. You can override this by dropping the ".sample" from the script,
-# editing it, committing, and pushing the result to the "ci-config" branch of
-# your repository:
-#
-#   git checkout -b ci-config
-#   cp allow-ref.sample allow-ref
-#   $EDITOR allow-ref
-#   git add allow-ref
-#   git commit -am "implement my ci preferences"
-#   git push
-#
-# This script will then be run when any refs are pushed to that repository. It
-# gets the fully qualified refname as the first argument, and should exit with
-# success only for refs for which you want to run CI.
-
-case "$1" in
-# allow one-off tests by pushing to "for-ci" or "for-ci/mybranch"
-refs/heads/for-ci*) true ;;
-# always build your integration branch
-refs/heads/my-integration-branch) true ;;
-# don't build any other branches or tags
-*) false ;;
-esac