android: Add SigningConfig.fromProperties function

CHANGELOG.md

@@ -19,6 +19,19 @@ android {
 }
 ```
 
+### Introduce `SigningConfig.fromProperties` (Experimental)
+
+It is common practice to store keystore credentials in `.properties` file.
+This extension lets you apply configurations from a property file.
+
+```kotlin
+android {
+    signingConfigs.getByName<SigningConfig>("debug") {
+        fromProperties(file("cert/debug.properties"))
+    }
+}
+```
+
 ### :warning: BREAKING CHANGES
 
 - **common:** Deprecate `redmadrobot.jvmTarget` with deprecation level `Error`.

infrastructure-android/src/main/kotlin/dsl/Signing.kt

@@ -0,0 +1,29 @@
+package dsl
+
+import com.android.build.api.dsl.SigningConfig
+import org.gradle.api.Incubating
+import java.io.File
+import java.util.*
+
+/**
+ * Applies signature configuration from the specified [propertiesFile].
+ *
+ * The file content should have the following format:
+ * ```
+ * store_file=[relative path to keystore file]
+ * store_password=[keystore password]
+ * key_alias=[the alias of the needed key]
+ * key_password=[the password for the specified alias]
+ * ```
+ */
+@Incubating
+public fun SigningConfig.fromProperties(propertiesFile: File) {
+    val directory = propertiesFile.parentFile
+    val properties = Properties()
+    propertiesFile.inputStream().use(properties::load)
+
+    storeFile = File(directory, properties.getProperty("store_file"))
+    storePassword = properties.getProperty("store_password")
+    keyAlias = properties.getProperty("key_alias")
+    keyPassword = properties.getProperty("key_password")
+}