DTLS PASSIVE currently not working

[nuessgens]

Description

We tried to "mimic" a browser for some kind of (unit) test by using DtlsControlImpl in PASSIVE mode

       DtlsControlImpl dtlsControl = new DtlsControlImpl(); 
        dtlsControl.registerUser(...);
        dtlsControl.setSetup(DtlsControl.Setup.PASSIVE);
        dtlsControl.start(MediaType.AUDIO);

This seems not to work.

Current behavior

We receive the following exception on the "PASSIVE" (/ hence server) side

 Failed to accept a connection from a DTLS client! Received fatal alert 70.
org.bouncycastle.tls.TlsFatalAlert: protocol_version(70)
	at org.bouncycastle.tls.AbstractTlsServer.getServerVersion(Unknown Source)
	at org.bouncycastle.tls.DTLSServerProtocol.generateServerHello(Unknown Source)
	at org.bouncycastle.tls.DTLSServerProtocol.serverHandshake(Unknown Source)
	at org.bouncycastle.tls.DTLSServerProtocol.accept(Unknown Source)
	at org.bouncycastle.tls.DTLSServerProtocol.accept(Unknown Source)
	at org.jitsi.impl.neomedia.transform.dtls.DtlsPacketTransformer.runInConnectThread(DtlsPacketTransformer.java:987)
	at org.jitsi.impl.neomedia.transform.dtls.DtlsPacketTransformer$1.run(DtlsPacketTransformer.java:1196)

Expected Behavior

By investigating with wireshark the client (also libjitsi) is announcing "DTLS 1.2" in the client_hello
But the TlsServerImpl is not overridng getSupportedVersions()
So the bouncycastle default of AbstractTlsPeer is effectivly used which returns "TLS 1.2, TLS 1.3" (which does not match DTLS at all).

I guess such capability is not working since the refactoring for DTLS 1.2
daabbbf#diff-30f47ad6700b3852583ec377401c7d040b0df6ecb2ed5e38ccb90f076373f48a
See the removal of previous overriden methods for getMinimumVersion() and getMaximumVersion() where explicitly "DTLS 1.0" was returned.

Possible Solution

We locally changed TlsServerImpl to override getSupportedVersions() and return "DTLS 1.2" only (getMinimumVersion() and getMaximumVersion() seem not to exisit in bouncycastle anymore)
That alone was not enough. We changed some more aspects regarding getRSASignerCredentials() and getCertificateRequest()

With the changes mentioned above our "test-setup" works: One side DtlsControlImpl in PASSIVE mode the other side (the actual code under test) with DtlsControlImpl in ACTIVE mode.

I can create a pull-request if desired (or provide a patch) but I'm not 100% sure of the implications of the changes we did to TlsServerImpl.