Example of declaring Android signing configs using Gradle Kotlin DSL

build.gradle.kts

android {
    signingConfigs {
        getByName("debug") {
            keyAlias = "debug"
            keyPassword = "my debug key password"
            storeFile = file("/home/miles/keystore.jks")
            storePassword = "my keystore password"
        }
        create("release") {
            keyAlias = "release"
            keyPassword = "my release key password"
            storeFile = file("/home/miles/keystore.jks")
            storePassword = "my keystore password"
        }
    }
    compileSdkVersion(28)
    defaultConfig {
        applicationId = "com.mileskrell.someneatapp"
        minSdkVersion(19)
        targetSdkVersion(28)
        versionCode = 1
        versionName = "1.0"
        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        getByName("release") {
            isMinifyEnabled = false
            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
            signingConfig = signingConfigs.getByName("release")
            isDebuggable = false
        }
        getByName("debug") {
            signingConfig = signingConfigs.getByName("debug")
            isDebuggable = true
        }
    }
}

Using keystore.properties files (create it in project root, gitignored)

Contents of keystore.properties

storePassword=mypass
keyPassword=mypass
keyAlias=key0

In app module build.gradle.kts

...

    defaultConfig {
        applicationId = "com.myapp"
        minSdk = 24
        targetSdk = 34
        versionCode = 2
        versionName = "1.1"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables {
            useSupportLibrary = true
        }
    }

    val keystorePropertiesFile = rootProject.file("keystore.properties")
    val keystoreProperties = Properties().apply {
        load(FileInputStream(keystorePropertiesFile))
    }
    signingConfigs {
        create("release") {
            storeFile = file("$rootDir/keystore.jks")
            storePassword = keystoreProperties["storePassword"] as String
            keyAlias = keystoreProperties["keyAlias"] as String
            keyPassword = keystoreProperties["keyPassword"] as String
        }

    }

    buildTypes {
        release {
            isMinifyEnabled = true
            isShrinkResources = true
            isDebuggable = true
            signingConfig = signingConfigs["release"]
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
    
    ...