grpc-spring: TLS not working with openJDK8

Not sure, if this is the right forum, but i failed to use TLS.

When connecting, i get

Caused by: javax.net.ssl.SSLHandshakeException: General OpenSslEngine problem
	at io.netty.handler.ssl.ReferenceCountedOpenSslContext$AbstractCertificateVerifier.verify(ReferenceCountedOpenSslContext.java:629) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.internal.tcnative.SSL.readFromSSL(Native Method) ~[netty-tcnative-boringssl-static-2.0.20.Final.jar:2.0.20.Final]
	at io.netty.handler.ssl.ReferenceCountedOpenSslEngine.readPlaintextData(ReferenceCountedOpenSslEngine.java:488) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.ReferenceCountedOpenSslEngine.unwrap(ReferenceCountedOpenSslEngine.java:1036) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.ReferenceCountedOpenSslEngine.unwrap(ReferenceCountedOpenSslEngine.java:1144) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.SslHandler$SslEngineType$1.unwrap(SslHandler.java:211) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1297) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1199) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1243) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:489) ~[netty-codec-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:428) ~[netty-codec-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:265) ~[netty-codec-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1434) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:965) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:628) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:563) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:480) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:442) ~[netty-transport-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884) ~[netty-common-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.29.Final.jar:4.1.29.Final]
	at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_181]
Caused by: java.lang.IllegalArgumentException: TLSv1.3
	at sun.security.ssl.ProtocolVersion.valueOf(ProtocolVersion.java:187) ~[na:1.8.0_181]
	at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:258) ~[na:1.8.0_181]
	at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:136) ~[na:1.8.0_181]
	at io.netty.handler.ssl.ReferenceCountedOpenSslClientContext$ExtendedTrustManagerVerifyCallback.verify(ReferenceCountedOpenSslClientContext.java:237) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	at io.netty.handler.ssl.ReferenceCountedOpenSslContext$AbstractCertificateVerifier.verify(ReferenceCountedOpenSslContext.java:625) ~[netty-handler-4.1.29.Final.jar:4.1.29.Final]
	... 26 common frames omitted

Looking at ProtocolVersion (in openJDK8) indeed reveals:

    private static ProtocolVersion valueOf(int var0) {
        if (var0 == SSL30.v) {
            return SSL30;
        } else if (var0 == TLS10.v) {
            return TLS10;
        } else if (var0 == TLS11.v) {
            return TLS11;
        } else if (var0 == TLS12.v) {
            return TLS12;
        } else if (var0 == SSL20Hello.v) {
            return SSL20Hello;
        } else {
            int var1 = var0 >>> 8 & 255;
            int var2 = var0 & 255;
            return new ProtocolVersion(var0, "Unknown-" + var1 + "." + var2);
        }
    }

Is there a way to use TLS1.2?

Setup:

Server and Client run on openjdk8. I am using boringssl-static on both sides

   <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-tcnative-boringssl-static</artifactId>
      <version>2.0.20.Final</version>
    </dependency>

Client properties:

grpc.client.x.port=9443
grpc.client.x.host=localhost
grpc.client.x.security.trustCertCollectionPath=src/etc/certificates/trusted-servers/localhost.crt
grpc.client.x.security.authorityOverride=localhost

Server properties:

grpc.server.port=9443
grpc.server.security.enabled=true
grpc.server.security.certificateChainPath=src/etc/certificates/localhost.crt
grpc.server.security.privateKeyPath=src/etc/certificates/localhost.key