Why do I receive an SSL handshake failure when using the Kafka 2.x client with Heroku Kafka?

Issue

When using a Kafak 2.x Java client in a producer or consumer, when attempting to produce or consumer messages you receive an SSL handshake failure, such as the following:

org.apache.kafka.common.errors.SslAuthenticationException: SSL handshake failed
Caused by: javax.net.ssl.SSLHandshakeException: General SSLEngine problem
	at sun.security.ssl.Handshaker.checkThrown(Handshaker.java:1529)
	at sun.security.ssl.SSLEngineImpl.checkTaskThrown(SSLEngineImpl.java:535)
	at sun.security.ssl.SSLEngineImpl.writeAppRecord(SSLEngineImpl.java:1214)
	at sun.security.ssl.SSLEngineImpl.wrap(SSLEngineImpl.java:1186)
	at javax.net.ssl.SSLEngine.wrap(SSLEngine.java:469)
	at org.apache.kafka.common.network.SslTransportLayer.handshakeWrap(SslTransportLayer.java:439)
	at org.apache.kafka.common.network.SslTransportLayer.doHandshake(SslTransportLayer.java:304)
	at org.apache.kafka.common.network.SslTransportLayer.handshake(SslTransportLayer.java:258)
	at org.apache.kafka.common.network.KafkaChannel.prepare(KafkaChannel.java:125)
	at org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:487)
	at org.apache.kafka.common.network.Selector.poll(Selector.java:425)
	at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:510)
	at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:239)
	at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:163)
	at java.lang.Thread.run(Thread.java:748)
Caused by: javax.net.ssl.SSLHandshakeException: General SSLEngine problem
	at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
	at sun.security.ssl.SSLEngineImpl.fatal(SSLEngineImpl.java:1728)
	at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:330)
	at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:322)
	at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1614)
	at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:216)
	at sun.security.ssl.Handshaker.processLoop(Handshaker.java:1052)
	at sun.security.ssl.Handshaker$1.run(Handshaker.java:992)
	at sun.security.ssl.Handshaker$1.run(Handshaker.java:989)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.security.ssl.Handshaker$DelegatedTask.run(Handshaker.java:1467)
	at org.apache.kafka.common.network.SslTransportLayer.runDelegatedTasks(SslTransportLayer.java:393)
	at org.apache.kafka.common.network.SslTransportLayer.handshakeUnwrap(SslTransportLayer.java:473)
	at org.apache.kafka.common.network.SslTransportLayer.doHandshake(SslTransportLayer.java:331)
	... 8 more
Caused by: java.security.cert.CertificateException: No name matching <redacted> found
	at sun.security.util.HostnameChecker.matchDNS(HostnameChecker.java:231)
	at sun.security.util.HostnameChecker.match(HostnameChecker.java:96)
	at sun.security.ssl.X509TrustManagerImpl.checkIdentity(X509TrustManagerImpl.java:455)
	at sun.security.ssl.X509TrustManagerImpl.checkIdentity(X509TrustManagerImpl.java:436)
	at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:252)
	at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:136)
	at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1601)

Resolution

This error is due to the ssl.endpoint.identification.algorithm configuration option being set to https, enabling hostname verification, and is the default for Kafka 2.x clients. This needs to be set to an empty string to be compatible with Heroku Kafka.

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