Using GitHub, I hardly managed credential/identity issues:

• I tried to configure the repository with various URLs/protocols which all work fine inside jobs but not for that plugin, always raising the issue below
• The server fails at committing because of

  hudson.plugins.scm_sync_configuration.ScmSyncConfigurationBusiness synchronizeFile
  INFO: Synchronizing file [jobs/nuxeo/config.xml] to SCM ...
  hudson.plugins.scm_sync_configuration.SCMManipulator checkinFiles
  SEVERE: [checkinFiles] Problem during commit of [[jobs/nuxeo/config.xml]] : 
  *** Please tell me who you are.
  
  Run
  
    git config --global user.email "you@example.com"
    git config --global user.name "Your Name"
  
  to set your account's default identity.
  Omit --global to set the identity only in this repository.
  
  fatal: empty ident  <hudson@someslave.in.nuxeo.com> not allowed

• setting global config doesn't solve the issue
• of course, those settings are already configured in the Git section
• finally, defining those values as local settings worked

The main issues are:

• the error message is wrong,
• since the fix requires the repository to exist and that repository is created/deleted by the plugin, it cannot be properly configured without raising the issue before (which is an issue when working with a lot of jobs),
• when the URLs fails at login (not for commit but for pull/push), the Jenkins server becomes unresponsive (I had to manually kill the git processes).

I don't know exactly what comes from the Git&GitHub plugins or JGit but it seems the scm_sync plugin is not using all available information, especially the user.email and user.name.

There should be a "test" button in the configuration to avoid starting initialization with repetitive failures.