Introduce CI build signing

We've done no signing of any Skyline APKs to date which causes issues regarding authenticity of any APKs as they could be entirely unofficial builds which have not been vetted by the team. Additionally, the different keys remove the ability to reinstall a different build successively as Android checks for matching signatures before installing an APK.

.github/workflows/ci.yml

@@ -45,7 +45,16 @@ jobs:
           name: lint-result.html
           path: app/build/reports/lint-results-debug.html
 
+      - name: Decode Keystore
+        env:
+          KEYSTORE_ENCODED: ${{ secrets.KEYSTORE }}
+        run: echo $KEYSTORE_ENCODED | base64 --decode > "$HOME/keystore.jks"
+
       - name: Android Assemble
+        env:
+          SIGNING_STORE_PASSWORD: ${{ secrets.SIGNING_STORE_PASSWORD }}
+          SIGNING_KEY_ALIAS: ${{ secrets.SIGNING_KEY_ALIAS }}
+          SIGNING_KEY_PASSWORD: ${{ secrets.SIGNING_KEY_PASSWORD }}
         run: ./gradlew --stacktrace assemble
 
       - name: Upload Debug APK

app/build.gradle

@@ -34,6 +34,15 @@ android {
         jvmTarget = javaVersion.toString()
     }
 
+    signingConfigs {
+        ci {
+            storeFile file("${System.getProperty("user.home")}/keystore.jks")
+            storePassword System.getenv("SIGNING_STORE_PASSWORD")
+            keyAlias System.getenv("SIGNING_KEY_ALIAS")
+            keyPassword System.getenv("SIGNING_KEY_PASSWORD")
+        }
+    }
+
     buildTypes {
         release {
             debuggable true
@@ -45,13 +54,14 @@ android {
             minifyEnabled true
             shrinkResources true
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
-            signingConfig signingConfigs.debug
+            signingConfig = System.getenv("CI") ? signingConfigs.ci : signingConfigs.debug
         }
 
         debug {
             debuggable true
             minifyEnabled false
             shrinkResources false
+            signingConfig = System.getenv("CI") ? signingConfigs.ci : signingConfigs.debug
         }
     }