Add docker build and push to docker hub

.github/workflows/ci.yml

@@ -81,3 +81,29 @@ jobs:
       # Ensure proto generation doesn't depend on external packages.
       - name: Verify proto
         run: make verify-proto
+
+  docker:
+    name: Docker
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Determine tag
+        uses: haya14busa/action-cond@v1
+        id: imagetag
+        with:
+          cond: ${{ github.event_name == 'pull_request' }}
+          if_true: ${{ github.sha }}
+          if_false: "master"
+
+      - name: Build
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+          repository: dexidp/dex
+          tags: ${{ steps.imagetag.outputs.value }}
+          add_git_labels: true
+          push: ${{ github.event_name == 'push' }}

.github/workflows/release.yml

+name: Release
+
+on:
+  push:
+    tags:
+      - "v[0-9]+.[0-9]+.[0-9]+"
+
+jobs:
+  docker:
+    name: Docker
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Build and push image
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+          repository: dexidp/dex
+          tags: latest
+          tag_with_ref: true
+          add_git_labels: true