Add github workflow

.github/workflows/php.yml

@@ -0,0 +1,58 @@
+name: PHP Composer
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  install:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate --strict
+
+      - name: Cache Composer packages
+        id: composer-cache
+        uses: actions/cache@v3
+        with:
+          path: vendor
+          key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-php-
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress
+
+  phpstan:
+    runs-on: ubuntu-latest
+    needs: install
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Run PHPStan
+        run: composer run-script phpstan
+
+  phpcs:
+    runs-on: ubuntu-latest
+    needs: install
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Run PHP Code Sniffer
+        run: composer run-script phpcs
+
+  phpunit:
+    runs-on: ubuntu-latest
+    needs: install
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Run unit tests
+        run: composer run-script phpunit
+

composer.json

@@ -3,6 +3,7 @@
   "description": "Client for communication with Bank iD services",
   "type": "library",
   "minimum-stability": "dev",
+  "license": "MIT",
   "prefer-stable": true,
   "authors": [
     {