android {
    buildFeatures {
        buildConfig = true  // これが必要
    } 
}

interface BindPropertyScope {
    fun stringConfigField(name: String, default: String = "")
    fun booleanConfigField(name: String, default: Boolean = false)
    fun stringResource(name: String, default: String = "")
}

fun VariantDimension.bindProperty(configure: BindPropertyScope.() -> Unit) {
    object: BindPropertyScope {
        override fun stringConfigField(name: String, default: String) {
            val value = (project.properties[name] as? String) ?: default
            buildConfigField("String", name, "\"$value\"")
        }
        override fun booleanConfigField(name: String, default: Boolean) {
            val value = (project.properties[name] as? String)?.toBoolean() ?: default
            buildConfigField("Boolean", name, value.toString())
        }
        override fun stringResource(name: String, default: String) {
            val value = (project.properties[name] as? String) ?: default
            resValue("string", name, value)
        }
    }.configure()
}

android {
    // ..
    defaultConfig {
        // ...
        bindProperty {
            stringConfigField("FOO_TOKEN")
            booleanConfigField("FOO_ENABLED", default = true)
            stringResource("BAR_URL")
        }
    }
}