Android Kotlin Proguard Obfuscation of Kotlin Default Impl

Question

I use Android + Kotlin + Proguard

Code

inferface Authentication {
 val authenticated: Boolean
 val lastAuthentication: Instant

 fun authenticate(force: Boolean = false): Flow<Event>
 suspend fun revokeAccess() 
}

And an implementation of that interface

internal sealed class AuthenticationInternal(
 private val trustProvider: TrustProvider) : Authentication {
 override val authenticated: Boolean
    get() = trustProvider.authenticatedBefore()

 override val lastAuthentication: Instant
    get() = trustProvider.getLastAuthenticatedTime()

 override fun authenticate() = flow {
    trustProvider.checkIntegrity()
    emitAll(internalAuthenticate())
 }.flowOn(Dispatchers.Default)

 override suspend fun revokeAccess() {
    trustProvider.revokeAccess()
 }
}

-> During Kotlin Annotation Processing this interface gets (as expected) a default implementation:

Kotlin generated code:

Class: Authentication$DefaultImpls.dex

-> Now my issue: Since this class is generated and not reachable from Kotlin code, how can I keep this class using progurard.

In my release build, this class is put out of the release dex and the application crashes with an RuntimeException.

Note: Adding this to the proguard mappings file: -keep class com.my.package.AuthenticationInternal$DefaultImpls { *; } will not work, since it is not reachable

How can I keep kapt-generated classes with proguard?