Public HTTPS

When using our Http2Client to communication with public API with CA-signed certificates, we have to find a way to download the certificate from the site and put it into our client.truststore file in order to establish TLS connection to the site if you cannot get the certificate from the right channel.

There are multiple options to do that, and the simple one is from the browser; however, the certificate downloaded from the browser might not be completed as we need the entire chain to verify the certificate during the handshake.

Here is a command line to do that.

openssl s_client -showcerts -connect us-east-1.online.tableau.com:443 </dev/null 2>/dev/null|openssl x509 -outform PEM >tableau.pem

Once you have downloaded the certificate, you can test it with wget command line.

wget https:/us-east-1.online.tableau.com --ca-certificate=tableau.pem

Now you can import it into the client.truststore file.

keytool -v -import -file tableau.pem -alias tableaucrt -keystore client.truststore 

For other keytool commands and options, please refer to keytool document.

After the client.truststore is modified, you need to use Http2Client to access the target server. There are numeric examples that can be found in light-example-4j/client and all the test cases.

Please note that you need to set the host header for all the requests to HTTP/1.1 servers.

request.getRequestHeaders().put(Headers.HOST, "localhost");

To see the demo application source code which accesses tableau server, please refer to https://github.com/networknt/light-example-4j/tree/master/client/tableau

For debugging your TLS connection, please refer to Debugging SSL/TLS Connections

Please note that download client certificate might not work all the time as the server might be behind a proxy which has its certificate and the proxy is set up as TLS passthrough. In that case, the certificate downloaded is for the proxy server and the real server will reject your certificate during the handshake. This happens with most Kubernetes cluster or OpenShift cluster.