Add CI setup

This will also build the PHARs instead of building them locally.

.github/workflows/ci.yml

@@ -0,0 +1,79 @@
+name: Continuous Integration
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  tests:
+    strategy:
+      matrix:
+        include:
+          - operating-system: 'ubuntu-latest'
+            php-version: '8.1'
+
+    name: PHP ${{ matrix.php-version }} ${{ matrix.job-description }}
+
+    runs-on: ${{ matrix.operating-system }}
+
+    steps:
+      - name: Set git to use LF
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.eol lf
+
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          ini-values: zend.assertions=1, assert.exception=1
+        env:
+          update: true
+
+      - name: Get Composer cache directory
+        id: composer-cache
+        run: echo "dir=$(composer config cache-dir)" >> $GITHUB_OUTPUT
+        shell: bash
+
+      - name: Cache dependencies
+        uses: actions/cache@v3
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: composer-${{ runner.os }}-${{ matrix.php-version }}-${{ hashFiles('**/composer.*') }}-${{ matrix.composer-flags }}
+          restore-keys: |
+            composer-${{ runner.os }}-${{ matrix.php-version }}-${{ hashFiles('**/composer.*') }}-
+            composer-${{ runner.os }}-${{ matrix.php-version }}-
+            composer-${{ runner.os }}-
+            composer-
+
+      - name: Install dependencies
+        uses: nick-invision/retry@v2
+        with:
+          timeout_minutes: 5
+          max_attempts: 5
+          retry_wait_seconds: 30
+          command: |
+            composer update --optimize-autoloader --no-interaction --no-progress ${{ matrix.composer-flags }}
+            composer info -D
+
+      - name: Run tests
+        run: vendor/bin/phpunit ${{ matrix.phpunit-flags }}
+
+      - name: Run style fixer
+        env:
+          PHP_CS_FIXER_IGNORE_ENV: 1
+        run: vendor/bin/php-cs-fixer --diff --dry-run -v fix
+        if: matrix.php-cs-fixer != 'none'
+
+      - name: Build phar
+        run: php -dphar.readonly=0 vendor/bin/phar-builder package
+
+      - name: Upload phar
+        uses: actions/upload-artifact@v3
+        with:
+          name: acme-client.phar
+          path: |
+            build/acme-client.phar