Load a x509 cert + rsa key and x509 ca and create an sslcontext in java using jruby. This took me a few hours to figure out since I wasn't super familiar with java, but here you go! Btw, you'll notice I'm using bouncycastle which is fine because it's a dependency of jruby-openssl. So as long as you require "openssl" this should work out of the box.

tls_cert_key_and_ca_jruby.rb

require "openssl"

def create_ssl_context(options)
  # Create our certs and key converters to go from bouncycastle to java.
  cert_converter = org.bouncycastle.cert.jcajce.JcaX509CertificateConverter.new
  key_converter = org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter.new

  # Load the certs and keys.
  tls_ca_cert = cert_converter.getCertificate(read_pem_object_from_file(options[:tls_ca_cert]))
  tls_client_cert = cert_converter.getCertificate(read_pem_object_from_file(options[:tls_client_cert]))
  tls_client_key = key_converter.getKeyPair(read_pem_object_from_file(options[:tls_client_key]))

  # Setup the CA cert.
  ca_key_store = java.security.KeyStore.getInstance(java.security.KeyStore.getDefaultType)
  ca_key_store.load(nil, nil)
  ca_key_store.setCertificateEntry("ca-certificate", tls_ca_cert)
  trust_manager = javax.net.ssl.TrustManagerFactory.getInstance(javax.net.ssl.TrustManagerFactory.getDefaultAlgorithm)
  trust_manager.init(ca_key_store)

  # Setup the cert / key pair.
  client_key_store = java.security.KeyStore.getInstance(java.security.KeyStore.getDefaultType)
  client_key_store.load(nil, nil)
  client_key_store.setCertificateEntry("certificate", tls_client_cert)
  certificate_java_array = [tls_client_cert].to_java(java.security.cert.Certificate)
  empty_password = [].to_java(:char)
  client_key_store.setKeyEntry("private-key", tls_client_key.getPrivate, empty_password, certificate_java_array)
  key_manager = javax.net.ssl.KeyManagerFactory.getInstance(javax.net.ssl.KeyManagerFactory.getDefaultAlgorithm)
  key_manager.init(client_key_store, empty_password)

  # Create ssl context.
  context = javax.net.ssl.SSLContext.getInstance("TLSv1.2")
  context.init(key_manager.getKeyManagers, trust_manager.getTrustManagers, nil)
  context
end