How to troubleshoot the connection with the proxy on Jenkins?

Symptoms

How to troubleshooting connection issues with the proxy on Jenkins

Diagnosis/Treatment

We recommend you create a logger with org.apache.commons.httpclient and then click on Validate Proxy.

Then, you might get a stacktrace like the one below, which suggest that your proxy is using NTLM authentication model.

Dec 11, 2015 11:46:37 AM SEVERE org.apache.commons.httpclient.HttpMethodDirector authenticate
Credentials cannot be used for NTLM authentication: org.apache.commons.httpclient.UsernamePasswordCredentials
org.apache.commons.httpclient.auth.InvalidCredentialsException: Credentials cannot be used for NTLM authentication: org.apache.commons.httpclient.UsernamePasswordCredentials
at org.apache.commons.httpclient.auth.NTLMScheme.authenticate(NTLMScheme.java:332)
at