Getting passwords for signing from file or environment

build.gradle

task askForPasswords << {
    def storePass
    def keyAlias
    def keyPass

    def keystorePropertiesFile = new File("../keystore/keystore.properties")
    println keystorePropertiesFile.absolutePath
    if (keystorePropertiesFile.exists()) {
        println "Loading keystore passwords from property file..."
        Properties properties = new Properties()
        properties.load(new FileInputStream(keystorePropertiesFile))

        println properties.getProperty('keyAlias')
        storePass = properties['storePassword']
        keyAlias = properties['keyAlias']
        keyPass = properties['keyPassword']
    } else if (System.getenv("KEY_ALIAS") != null) {
        println "Getting keystore passwords from environment variables..."
        storePass = System.getenv("STORE_PASS")
        keyAlias = System.getenv("KEY_ALIAS")
        keyPass = System.getenv("KEY_PASS")
    }

    android.signingConfigs.release.storePassword = storePass
    android.signingConfigs.release.keyAlias = keyAlias
    android.signingConfigs.release.keyPassword = keyPass
}

tasks.whenTaskAdded {
    theTask ->
        if (theTask.name.matches("package.*Release")) {
            theTask.dependsOn "askForPasswords"
        }
}