I've been trying to get eGit working with Eclipse 4.6.3 (IBM Rational Developer 9.6.0.6) but keep hitting the same error when either trying to pull/push an existing Git repository or clone another using http.
Mostly the error specifics are hidden but if you examine the error in the Error Log view the following is observed:
It looks like the password authenticator is missing from the host eclipse or something similar.
I found the answer to this and am sharing the knowledge.
After investigating the supported software on IBM's website for Rational developer I saw that it claimed to be compatible with eGit version 4.5.0201609210915-r, alas the eclipse add new software links postfixed with -4.5 & -4.6 no longer functioned correctly however I was able to successfully install a compatible eGit (version 4.7.0.201704051617-r) with the following:
http://download.eclipse.org/egit/updates-4.7
-edit- Have just had success with the last of 4, version 4.11.0.201803080745r