based on https://gist.github.com/ankushg/8c0c3144318b1c17abb228d6211ba996

TlsSocketFactory.kt

package com.example.android.kotlincoroutines.ktor

import android.os.Build
import android.util.Log
import okhttp3.OkHttpClient
import okhttp3.TlsVersion
import java.io.IOException
import java.net.InetAddress
import java.net.Socket
import java.net.UnknownHostException
import java.security.KeyStore
import javax.net.ssl.*

/**
 * Extension function for TLS Support on pre-lollipop.
 */
private val trustManager by lazy {
    val trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm())
    trustManagerFactory.init(null as KeyStore?)
    trustManagerFactory.trustManagers
            .first { it is X509TrustManager } as X509TrustManager
}

fun OkHttpClient.Builder.enableTlsOnPreLollipop() = apply {
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
        try {
            val sslContext = SSLContext.getInstance("TLS")
            sslContext.init(null, arrayOf(trustManager), null)
            sslSocketFactory(Tls12SocketFactory(sslContext.socketFactory), trustManager)
        } catch (e: Exception) {
            Log.e("Tls12SocketFactory", "Error while setting TLS compatibility")
        }
    }
}

class Tls12SocketFactory(private val delegate: SSLSocketFactory) : SSLSocketFactory() {

    /**
     * Forcefully adds [TlsVersion.TLS_1_2] as an enabled protocol if called on an [SSLSocket]
     *
     * @return the (potentially modified) [Socket]
     */
    private fun Socket.patchForTls12(): Socket {
        return (this as? SSLSocket)?.apply {
            enabledProtocols += TlsVersion.TLS_1_1.javaName()
            enabledProtocols += TlsVersion.TLS_1_2.javaName()
        } ?: this
    }

    override fun getDefaultCipherSuites(): Array<String> {
        return delegate.defaultCipherSuites
    }

    override fun getSupportedCipherSuites(): Array<String> {
        return delegate.supportedCipherSuites
    }

    @Throws(IOException::class)
    override fun createSocket(s: Socket, host: String, port: Int, autoClose: Boolean): Socket? {
        return delegate.createSocket(s, host, port, autoClose)
                .patchForTls12()
    }

    @Throws(IOException::class, UnknownHostException::class)
    override fun createSocket(host: String, port: Int): Socket? {
        return delegate.createSocket(host, port)
                .patchForTls12()
    }

    @Throws(IOException::class, UnknownHostException::class)
    override fun createSocket(host: String, port: Int, localHost: InetAddress, localPort: Int): Socket? {
        return delegate.createSocket(host, port, localHost, localPort)
                .patchForTls12()
    }

    @Throws(IOException::class)
    override fun createSocket(host: InetAddress, port: Int): Socket? {
        return delegate.createSocket(host, port)
                .patchForTls12()
    }

    @Throws(IOException::class)
    override fun createSocket(address: InetAddress, port: Int, localAddress: InetAddress, localPort: Int): Socket? {
        return delegate.createSocket(address, port, localAddress, localPort)
                .patchForTls12()
    }
}